Rollup merge of rust-lang#88387 - ehuss:remove-rustfix-tests, r=Mark-Simulacrum

Remove vestigial rustfix tests.

The directory `src/test/rustfix` is not actually tested. It looks like a mistake was made when rustfix tests were originally introduced in rust-lang#50084.  In commit 6f2d023 they were moved to `src/test/ui`, but the tests in the original directory weren't deleted.

Author: GuillaumeGomez