Rollup merge of rust-lang#128262 - DianQK:remove-unused-tests, r=saethlin

Delete `SimplifyArmIdentity` and `SimplifyBranchSame` tests

These two passes have already been deleted in rust-lang#107256. I'm not sure why tidy didn't catch it.

As regression tests, I didn't delete `tests/ui/mir/issue-66851.rs` and `tests/ui/mir/simplify-branch-same.rs`.

r? compiler

Author: tgross35