Auto merge of #108689 - compiler-errors:normalization-error-smaller, r=lcnr

Remove `NormalizationError::ConstantKind`

No longer in use by `TryNormalizeAfterErasingRegionsFolder` (as of #102355 / e8150fa60cc445de7a57db634deb0668880be593 it seems). It's making `LayoutError`, etc. kinda large -- that was noticed by `@zoxc.`

Author: bors