[Hexagon] Remove unused declaration adjustForCalleeSavedRegsSpillCall (NFC)

The function definition was removed on Apr 23, 2015 in commit
876a19d, but the declaration has
remained since.

Author: kazutakahirata

llvm/lib/Target/Hexagon/HexagonFrameLowering.h

@@ -129,8 +129,6 @@ class HexagonFrameLowering : public TargetFrameLowering {
   void insertCFIInstructionsAt(MachineBasicBlock &MBB,
       MachineBasicBlock::iterator At) const;
 
-  void adjustForCalleeSavedRegsSpillCall(MachineFunction &MF) const;
-
   bool expandCopy(MachineBasicBlock &B, MachineBasicBlock::iterator It,
       MachineRegisterInfo &MRI, const HexagonInstrInfo &HII,
       SmallVectorImpl<unsigned> &NewRegs) const;