Reverting NFC changes from r218050. Instead, the warning was disabled for GCC in r218059, so these changes are no longer required.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218062 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/SystemZ/SystemZTargetMachine.h

@@ -32,7 +32,6 @@ public:
                        CodeGenOpt::Level OL);
 
   // Override TargetMachine.
-  using LLVMTargetMachine::getSubtargetImpl;
   const SystemZSubtarget *getSubtargetImpl() const override {
     return &Subtarget;
   }