Rollup merge of #101435 - JakobDegen:bitwidth-tests, r=wesleywiser

Remove unnecessary `EMIT_MIR_FOR_EACH_BITWIDTH`

This commit removes the annotation only for those tests where the 32 bit and 64 bit files were exactly identical. I didn't touch anything in the `mir-opt/const` directory, since having this annotation there seems more principled, even if it doesn't make a difference.

This also removes four additional files related to the `separate_const_switch.rs` test. The associated annotations were removed in #100827 , but I forgot to remove the files as well. (#97564 is the issue tracking an automated check here)

r? ```@wesleywiser```

Author: matthiaskrgr

src/test/mir-opt/array-index-is-temporary.rs

@@ -7,7 +7,7 @@ unsafe fn foo(z: *mut usize) -> u32 {
     99
 }
 
-// EMIT_MIR_FOR_EACH_BIT_WIDTH
+
 // EMIT_MIR array_index_is_temporary.main.SimplifyCfg-elaborate-drops.after.mir
 fn main() {
     let mut x = [42, 43, 44];