[llvm] [NFC][AMDGPU][SIMemoryLegalizer] remove effectively empty function (PR #156806)

[Pierre van Houtryve via llvm-commits]

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@@ -443,10 +443,6 @@ class SIGfx90ACacheControl : public SIGfx7CacheControl {
                              SIAtomicScope Scope,
                              SIAtomicAddrSpace AddrSpace) const override;
 
-  bool enableStoreCacheBypass(const MachineBasicBlock::iterator &MI,
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Pierre-vh wrote:

Can you add a comment to make it clear it's unimplemented by choice, not by mistake ?
Maybe comment out the declaration + add a small comment to say no additional bits are needed in this case

https://github.com/llvm/llvm-project/pull/156806