Remove an outdated test

[WaffleLapkin]

This... is a weird test.

It has two impls:

• impl<T> From<Foo<T>> for Box<T> (commented out, more on that later), and
• impl<T> Into<Vec<T>> for Foo<T>

The idea of that test is to show that the first impl doesn't compile, but the second does, thus TryFrom should be using Into and not From (because Into is more general, since the From impl doesn't compile).

However:

1. The types are different -- Box vs Vec, which is significant b/c Box is fundamental
2. The commented out impl actually compiles! (which wasn't detected b/c it's commented out :\ )

Here is a table for compilation of the impls:

	Vec	Box
From	since 1.41.0	never
Into	always	not since 1.28

godbolt used to test this

Order of events:

1. in 1.28 the incoherent_fundamental_impls lint becomes deny by default (this is not mentioned in the changelog yay)
2. 1.32 changed absolutely nothing, even though this version is credited in the test
3. the test was added (I'm not exactly sure when) (see Change bounds on TryFrom blanket impl to use Into instead of From #56796)
4. in 1.41 coherence was relaxed to allow From+Vec to compile

To conclude: since 1.41 this test does nothing (and before that it was written in a way which did not detect this change). It looks to me like today (since 1.41) we could bound TryFrom impl with From (but now it'd be a useless breaking change of course).

Am I missing anything? Is there a useful version of this test that could be written?

[rustbot]

r? @davidtwco

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[jdonszelmann]

I've looked through the tests, and I can't find one (not even doc test) that tests the fact that try_from has a blanket impl for T: Into, etc. So maybe having some library test for that would be nice? This test on its own seems indeed useless though, since 1.41 definitely.

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