Revert "[indvars] Missing variables at Og (#88270)" (#93016)

This reverts commit 89e1f778.

https://github.com/llvm/llvm-project/pull/88270#discussion_r1609559724
https://github.com/llvm/llvm-project/pull/88270#discussion_r1609552972

Main concerns from @nikic are the interaction between the
'IndVars' and 'LoopDeletion' passes, increasing build times
and adding extra complexity.