Rollup merge of rust-lang#97570 - JakobDegen:dse-test, r=tmiasko

Fix TLS access mir opt test and remove stale files

Thanks `@pietroalbini` for noticing that the TLS test was not doing what it was supposed to. Switched to `PreCodegen` because `SimplifyCfg` does not run on opt level 0.

Also addresses the easy part of rust-lang#97564 .

r? rust-lang/mir-opt

Author: Dylan-DPC