[AMDGPU][Waitcnt] Remove obsolete waitcnt option

With the removal of the old waitcnt pass, the '-enable-si-insert-waitcnts' option is obsolete. Remove it.

Differential Revision: https://reviews.llvm.org/D47378

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@333303 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed