Remove #[static_assert]
Remove #[static_assert]

This was always a weird feature, and isn't being used in the compiler.
Static assertions should be done better than this.

This implements RFC #1096.

Fixes #13951
Fixes #23008
Fixes #6676

This is behind a feature gate, but that's still a

[breaking-change]

rust-lang/reference,rust-lang/reference