Remove unused private fields

[GMNGeoffrey]

Summary

Unused since https://reviews.llvm.org/D91762 and triggering
-Wunused-private-field

llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:365:13: error: private field 'GetArgTLS' is not used [-Werror,-Wunused-private-field]
  Constant *GetArgTLS;
            ^
llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp:366:13: error: private field 'GetRetvalTLS' is not used [-Werror,-Wunused-private-field]
  Constant *GetRetvalTLS;

[stephan.yichao.zhao]

Thank you.

llvm/lib/Transforms/Instrumentation/DataFlowSanitizer.cpp

class DataFlowSanitizer {
   IntegerType *ShadowTy;
   PointerType *ShadowPtrTy;
   IntegerType *IntptrTy;
   ConstantInt *ZeroShadow;
   ConstantInt *ShadowPtrMask;
   ConstantInt *ShadowPtrMul;
   Constant *ArgTLS;
   Constant *RetvalTLS;
-  Constant *GetArgTLS;
-  Constant *GetRetvalTLS;
   Constant *ExternalShadowMask;
   FunctionType *DFSanUnionFnTy;
   FunctionType *DFSanUnionLoadFnTy;
   FunctionType *DFSanUnimplementedFnTy;
   FunctionType *DFSanSetLabelFnTy;
   FunctionType *DFSanNonzeroLabelFnTy;
   FunctionType *DFSanVarargWrapperFnTy;
   FunctionType *DFSanCmpCallbackFnTy;