Removing DeadInstEliminationPass

DeadInstEliminationPass is like DeadCodeEliminationPass but it only does one pass through a function instead of iterating on users of eliminated instructions.

The reason I’d like to remove this is because it isn’t ported to the new pass manager, and it doesn’t seem very useful when DeadCodeEliminationPass exists. It also doesn’t have very many appearances in tests compared to DCE.

Removing in

Any objections?

Nothing comes to mind where DCE isn't a proper replacement, I'm in favor.

SGTM, this (like the old constprop pass) isn’t used by anything I’m aware of.