Rollup merge of rust-lang#134637 - compiler-errors:fx-test, r=fmease

Flatten effects directory now that it doesn't really test anything specific

These are just const trait tests now, after all.

There was one naming conflict between the aux-build `tests/ui/traits/const-traits/effects/auxiliary/cross-crate.rs` and `tests/ui/traits/const-traits/auxiliary/cross-crate.rs`. The former didn't really test anything useful since we no longer have an effect param, so I removed the test that owned it: `tests/ui/traits/const-traits/effects/no-explicit-const-params-cross-crate.rs`.

r? project-const-traits

Author: matthiaskrgr