[DebugInfo] Remove redefinition of 'getDPVAssignmentMarkers' (NFC)

llvm-project/llvm/include/llvm/IR/DebugInfo.h:239:31: error: redefinition of 'getDPVAssignmentMarkers'
inline SmallVector<DPValue *> getDPVAssignmentMarkers(const Instruction *Inst) {
                              ^
llvm-project/llvm/include/llvm/IR/DebugInfo.h:233:31: note: previous definition is here
inline SmallVector<DPValue *> getDPVAssignmentMarkers(const Instruction *Inst) {
                              ^