[Coroutines] Remove CoroElide from O0 pipeline

CoroElide pass works only when a post-split coroutine is inlined into another post-split coroutine.
In O0, there is no inlining after CoroSplit, and hence no CoroElide can happen.
It's useless to put CoroElide pass in the O0 pipeline and it will never be triggered (unless I miss anything).

Differential Revision: https://reviews.llvm.org/D105066