[AMDGPU] Remove GFX12 encoding hack (#78702)

This is no longer needed now that we have implemented GFX12 encoding for
all instructions.

Author: jayfoad

llvm/lib/Target/AMDGPU/SIInstrInfo.cpp

@@ -9136,12 +9136,6 @@ int SIInstrInfo::pseudoToMCOpcode(int Opcode) const {
 
   int MCOp = AMDGPU::getMCOpcode(Opcode, Gen);
 
-  // TODO-GFX12: Remove this.
-  // Hack to allow some GFX12 codegen tests to run before all the encodings are
-  // implemented.
-  if (MCOp == (uint16_t)-1 && Gen == SIEncodingFamily::GFX12)
-    MCOp = AMDGPU::getMCOpcode(Opcode, SIEncodingFamily::GFX11);
-
   // -1 means that Opcode is already a native instruction.
   if (MCOp == -1)
     return Opcode;