[AMDGPU] AMDGPUSetWavePriority: Remove unused variable NFC (#134069)

Fixes a13a51b (#130064)

Author: optimisan

llvm/lib/Target/AMDGPU/AMDGPUSetWavePriority.cpp

@@ -43,8 +43,6 @@ using MBBInfoSet = DenseMap<const MachineBasicBlock *, MBBInfo>;
 
 class AMDGPUSetWavePriority {
 public:
-  static char ID;
-
   bool run(MachineFunction &MF);
 
 private: