AMDGPU: Remove triple field from subtarget (#164208)

This is redundant and already exists in the base class, and
is also unused.

Author: arsenm

llvm/lib/Target/AMDGPU/GCNSubtarget.cpp

@@ -169,7 +169,6 @@ GCNSubtarget::GCNSubtarget(const Triple &TT, StringRef GPU, StringRef FS,
     : // clang-format off
     AMDGPUGenSubtargetInfo(TT, GPU, /*TuneCPU*/ GPU, FS),
     AMDGPUSubtarget(TT),
-    TargetTriple(TT),
     TargetID(*this),
     InstrItins(getInstrItineraryForCPU(GPU)),
     InstrInfo(initializeSubtargetDependencies(TT, GPU, FS)),

llvm/lib/Target/AMDGPU/GCNSubtarget.h

@@ -60,7 +60,6 @@ class GCNSubtarget final : public AMDGPUGenSubtargetInfo,
 
 protected:
   // Basic subtarget description.
-  Triple TargetTriple;
   AMDGPU::IsaInfo::AMDGPUTargetID TargetID;
   unsigned Gen = INVALID;
   InstrItineraryData InstrItins;