[Mips] Remove dead code

[chenwj]

Summary

I believe the role of ehDataReg has been replaced by MipsABIInfo::GetEhDataReg, thus removing the dead code.

[sdardis]

LGTM, I'm not seeing an implementation of that method or a callee.

[chenwj]

@sdardis I have no commit access. Please commit it for me, thanks.

lib/Target/Mips/MipsSEFrameLowering.h

bool spillCalleeSavedRegisters(MachineBasicBlock &MBB,
                                  MachineBasicBlock::iterator MI,
                                  const std::vector<CalleeSavedInfo> &CSI,
                                  const TargetRegisterInfo *TRI) const override;
 
   bool hasReservedCallFrame(const MachineFunction &MF) const override;
 
   void determineCalleeSaves(MachineFunction &MF, BitVector &SavedRegs,
                             RegScavenger *RS) const override;
-  unsigned ehDataReg(unsigned I) const;
 
 private:
   void emitInterruptEpilogueStub(MachineFunction &MF,
                                  MachineBasicBlock &MBB) const;
   void emitInterruptPrologueStub(MachineFunction &MF,
                                  MachineBasicBlock &MBB) const;
 };
 
 } // end namespace llvm
 
 #endif // LLVM_LIB_TARGET_MIPS_MIPSSEFRAMELOWERING_H