[llvm] [AMDGPU][SIInsertWaitcnts][NFC] Drop MaxCounter member variable (PR #181092)

[via llvm-commits]

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vporpo wrote:

This looks like it may change per MF, so shouldn't WCG make sure it uses the right IsExpertMode and MaxCounter per function?

https://github.com/llvm/llvm-project/pull/181092