[NFC] Delete the redundant member 'shouldEmitMoves' from DwarfCFIException class

The data member 'shouldEmitMoves' is only used in DwarfCFIException::beginFunction()
and 'shouldEmitCFI' in DwarfCFIExceptionBase serves its purpose.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D101155