Rollup merge of #102270 - Nilstrieb:delete-useless-benches, r=TaKO8Ki

Remove benches from `rustc_middle`

These benches benchmark rust langauge features and not the compiler, so they seem to be in the wrong place here. They also all take <1ns, making them pretty useless. Looking at their git history, they just seem to have been carried around for many, many years. This commit ends their journey.