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

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```