Allow unnormalized types in drop elaboration

[Nadrieril]

I work on a rustc driver that aims to extract the full polymorphic MIR of a crate. Currently the one thing I can't get is drop glue because it fails on unnormalizable types like the fields of Cow or NonZero.

This PR removes the one check for unnormalized types in drop elaboration. It's a span_delay_bug so only there to help catch mistakes. I think that's fine to remove? If something downstream relies on types being normalized the right approach is for MIR validation to check for normalized types, not that one random check.

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[rustbot]

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[rustbot]

⚠️ Warning ⚠️

• This PR is based on an upstream commit that is older than 28 days.

  It's recommended to update your branch according to the rustc-dev-guide.