Remove assert for unstable expectation IDs

[xFrednet]

The assert requires that the check_crate query was executed before HandlerInner is dropped. This will not always be the case and can cause ICEs.

Closes #94953

The ICE was introduced in #94670

[rust-highfive]

r? @Mark-Simulacrum

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[Mark-Simulacrum]

It is not obvious to me that removing the assert here is the right step, instead of fixing whatever is causing us to not handle the stashed IDs. I'm not very familiar with this infrastructure though so maybe r? @wesleywiser?

[wesleywiser]

It is not obvious to me that removing the assert here is the right step, instead of fixing whatever is causing us to not handle the stashed IDs.

Agreed, I think the assert is important, so we don't accidentally forget about stashed diagnostics leading to them never being displayed in some case. Without the assert, it will be difficult to track down why they aren't being emitted. If this is only happening with -Zunpretty=expanded, then I don't this bug is super urgent and it would be better to do the refactorings you mentioned and then solve this in a more principled manner.

[xFrednet]

I believe that this will remain a problem even with the planned refactorings. However, I'm okay with leaving the issue open and revisiting it later :). I'll close this PR meanwhile. :)