[AMDGPU] Delete dead code

[davide]

Summary

This seems to be unused (set but never used), and breaks my GCC7 build with -Werror.

[arsenm]

lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp

504

This was supposed to be the fast part if there are no calls. I can fix this tomorrow

lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp

 
   // If there are no calls, MachineRegisterInfo can tell us the used register
   // count easily.
-
-  MCPhysReg HighestVGPRReg = AMDGPU::NoRegister;
-  for (MCPhysReg Reg : reverse(AMDGPU::VGPR_32RegClass.getRegisters())) {
-    if (MRI.isPhysRegUsed(Reg)) {
-      HighestVGPRReg = Reg;
-      break;
-    }
-  }
-
   int32_t MaxVGPR = -1;
   int32_t MaxSGPR = -1;
   uint32_t CalleeFrameSize = 0;