Remove asm.demangle

[kazarmy]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository.
• I made sure to follow the project's coding style.
• I've documented every RZ_API function and struct this PR changes.
• I've added tests that prove my changes are effective (required for changes to RZ_API).
• I've updated the Rizin book with the relevant information (if needed).
• I've used AI tools to generate fully or partially these code changes and I'm sure the changes are not copyrighted by somebody else.

Detailed description

This pr removes asm.demangle since, as noted in #3543 (comment), it is never read by any part of the Rizin code.

Test plan

The change makes sense. All builds are green.

Closing issues

...

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 49.24%. Comparing base (c7dc9f4) to head (1296fa0).

Additional details and impacted files

Files with missing lines	Coverage Δ
librz/core/cconfig.c	80.27% <ø> (-0.01%)	⬇️
librz/main/rizin.c	49.79% <ø> (-0.06%)	⬇️

... and 8 files with indirect coverage changes

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[wargio]

@kazarmy you need to bump the project version