[AMDGPU] Remove hasDefinedInitializer (NFC)

The last use was removed on Sep 16, 2021 in commit
7a62a5b.

Author: kazutakahirata

llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp

@@ -1332,14 +1332,6 @@ void AMDGPUTargetLowering::ReplaceNodeResults(SDNode *N,
   }
 }
 
-bool AMDGPUTargetLowering::hasDefinedInitializer(const GlobalValue *GV) {
-  const GlobalVariable *GVar = dyn_cast<GlobalVariable>(GV);
-  if (!GVar || !GVar->hasInitializer())
-    return false;
-
-  return !isa<UndefValue>(GVar->getInitializer());
-}
-
 SDValue AMDGPUTargetLowering::LowerGlobalAddress(AMDGPUMachineFunction* MFI,
                                                  SDValue Op,
                                                  SelectionDAG &DAG) const {

llvm/lib/Target/AMDGPU/AMDGPUISelLowering.h

@@ -37,7 +37,6 @@ class AMDGPUTargetLowering : public TargetLowering {
 public:
   static unsigned numBitsUnsigned(SDValue Op, SelectionDAG &DAG);
   static unsigned numBitsSigned(SDValue Op, SelectionDAG &DAG);
-  static bool hasDefinedInitializer(const GlobalValue *GV);
 
 protected:
   SDValue LowerEXTRACT_SUBVECTOR(SDValue Op, SelectionDAG &DAG) const;