checker: clear all ref from autostr receiver_type

[kbkpbot]

This is a feature needed by PR #25857, which can make sure always generate auto str function like this:

pub fn (it main.Example) str() string 

instead of something like this :

pub fn (it &main.Example) str() string 
pub fn (it &&main.Example) str() string 

This should has no impact on current auto str mechanism.

[spytheman]

Is there a performance impact?

[kbkpbot]

Is there a performance impact?

I think it is acceptable.

 >  1           base            122.4ms ± σ:    0.6ms,  121.8ms… 123.2ms `./vold -no-parallel -o ohw.exe examples/hello_world.v`
    2     +0.6%   1.01x slower  123.1ms ± σ:    0.3ms,  122.7ms… 123.4ms `./vnew -no-parallel -o nhw.exe examples/hello_world.v`
>>>>>> size("          nhw.exe") - size("          ohw.exe") =     241912 -     241912 =          0
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 1/3, took: 13601.472 ms
 >  1           base            557.7ms ± σ:    3.0ms,  553.6ms… 560.8ms `./vold -check-syntax           cmd/v`
    2     +1.6%   1.02x slower  566.4ms ± σ:    1.9ms,  564.2ms… 568.8ms `./vnew -check-syntax           cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 2/3, took: 13585.045 ms
 >  1           base            560.0ms ± σ:    1.3ms,  558.3ms… 561.5ms `./vold -check-syntax           cmd/v`
    2     +1.1%   1.01x slower  566.3ms ± σ:    0.5ms,  565.7ms… 566.9ms `./vnew -check-syntax           cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 3/3, took: 13633.698 ms
 >  1           base            562.8ms ± σ:    1.3ms,  561.7ms… 564.6ms `./vold -check-syntax           cmd/v`
    2     +0.7%   1.01x slower  567.0ms ± σ:    0.8ms,  565.9ms… 567.6ms `./vnew -check-syntax           cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 1/3, took: 23452.253 ms
 >  1           base            963.1ms ± σ:    7.8ms,  952.0ms… 968.6ms `./vold -check                  cmd/v`
    2     +1.5%   1.02x slower  977.9ms ± σ:    1.9ms,  975.3ms… 979.7ms `./vnew -check                  cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 2/3, took: 23560.747 ms
 >  1           base            969.3ms ± σ:    2.4ms,  966.0ms… 971.2ms `./vold -check                  cmd/v`
    2     +0.9%   1.01x slower  977.8ms ± σ:    1.3ms,  976.7ms… 979.6ms `./vnew -check                  cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 3/3, took: 23474.061 ms
 >  1           base            971.4ms ± σ:    1.5ms,  969.3ms… 972.7ms `./vold -check                  cmd/v`
    2     +0.2%   1.00x slower  973.9ms ± σ:    0.3ms,  973.5ms… 974.2ms `./vnew -check                  cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 1/3, took: 36199.770 ms
 >  1           base           1492.8ms ± σ:    2.3ms, 1491.0ms…1496.0ms `./vold -no-parallel -o ov.c    cmd/v`
    2     +0.8%   1.01x slower 1504.3ms ± σ:    2.3ms, 1501.2ms…1507.0ms `./vnew -no-parallel -o nv.c    cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 2/3, took: 36229.166 ms
 >  1           base           1497.4ms ± σ:    1.9ms, 1495.3ms…1499.9ms `./vold -no-parallel -o ov.c    cmd/v`
    2     +0.1%   1.00x ~same~ 1498.9ms ± σ:    6.1ms, 1492.4ms…1507.1ms `./vnew -no-parallel -o nv.c    cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 3/3, took: 36156.163 ms
 >  1           base           1497.1ms ± σ:    4.7ms, 1491.5ms…1502.9ms `./vold -no-parallel -o ov.c    cmd/v`
    2     +0.0%   1.00x ~same~ 1497.3ms ± σ:    3.4ms, 1493.4ms…1501.8ms `./vnew -no-parallel -o nv.c    cmd/v`
>>>>>> size("             nv.c") - size("             ov.c") =    6941779 -    6941779 =          0
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 1/3, took: 42145.603 ms
 >  1           base           1739.0ms ± σ:    6.8ms, 1729.5ms…1744.6ms `./vold -no-parallel -o ov.exe  cmd/v`
    2     +0.8%   1.01x slower 1752.2ms ± σ:    1.9ms, 1749.8ms…1754.5ms `./vnew -no-parallel -o nv.exe  cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 2/3, took: 42145.245 ms
 >  1           base           1741.1ms ± σ:    3.1ms, 1736.9ms…1744.5ms `./vold -no-parallel -o ov.exe  cmd/v`
    2     +0.3%   1.00x slower 1747.0ms ± σ:    3.4ms, 1742.2ms…1749.7ms `./vnew -no-parallel -o nv.exe  cmd/v`
Summary after 1 series x 10 runs (%s are relative to first command, or `base`), discard maxs:  7, repeat: 3/3, took: 41990.621 ms
 >  1           base           1739.6ms ± σ:    0.7ms, 1739.1ms…1740.6ms `./vold -no-parallel -o ov.exe  cmd/v`
    2     +0.1%   1.00x ~same~ 1741.9ms ± σ:    7.4ms, 1733.5ms…1751.6ms `./vnew -no-parallel -o nv.exe  cmd/v`
>>>>>> size("           nv.exe") - size("           ov.exe") =   10484376 -   10484376 =          0
Done. Total time: 393.897432377 s.
==================================================================================================
Final summary for file diff sizes on their own branches:
>>>>>> size("    nhw_current.c") - size("     ohw_master.c") =      28170 -      28170 =          0
>>>>>> size("nhw_current_gcc.c") - size(" ohw_master_gcc.c") =      41256 -      41256 =          0
>>>>>> size("     nv_current.c") - size("      ov_master.c") =    6941779 -    6941612 =        167
>>>>>> size("             vnew") - size("             vold") =   10484374 -   10484095 =        279
==================================================================================================
Final summary for file diff sizes for generated files on the *current* branch:
>>>>>> size("            nhw.c") - size("            ohw.c") =      28170 -      28170 =          0
>>>>>> size("             nv.c") - size("             ov.c") =    6941779 -    6941779 =          0
>>>>>> size("          nhw.exe") - size("          ohw.exe") =     241912 -     241912 =          0
>>>>>> size("           nv.exe") - size("           ov.exe") =   10484376 -   10484376 =          0

[spytheman]

Thank you @kbkpbot 🙇🏻 .