Remove a test that never runs

[bjorn3]

The coretests crate doesn't have the debug_typeid feature, so this test will always be configured out.

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[compiler-errors]

This was added by @kpreid in #136148. @Mark-Simulacrum had some feelings about feature = "..." based gating in libcore/libstd.

I don't see much value in just removing the test if we're keeping all the other gated stuff in, though? I assume we should just fix the feature gating of coretest?

[kpreid]

To give some context, I probably originally wrote PR #136148 before the coretests split (#135937) was merged, so the test would have been in core itself and subject to its features.

I don't have any particular opinion on what should happen to this test, other than: won't we eventually want coretests to be able to test features of core, even if this one test is not highly valuable?

[Mark-Simulacrum]

I tend to agree that removing the test seems like the wrong approach to fixing this (we should want the test somewhere...). I don't have a strong opinion on how we try to test this functionality though.

[Mark-Simulacrum]

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