AMDGPU: Remove deprecated llvm.AMDGPU.kilp intrinsic

Summary: This is no longer used by mesa since its 18.0.0 release.

Reviewers: nhaehnle

Reviewed By: nhaehnle

Subscribers: arsenm, kzhuravl, wdng, yaxunl, dstuttard, tpr, llvm-commits, t-tye

Differential Revision: https://reviews.llvm.org/D45988

llvm-svn: 330775