[AMDGPU][Waitcnt] Remove the old waitcnt pass

Remove the old waitcnt pass ( si-insert-waits ), which is no longer maintained
and getting crufty

Differential Revision: https://reviews.llvm.org/D46448

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@331641 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed