[ObjCopy][NFC] Remove unneeded zero initialization

getNewMemBuffer has called memset.

Reviewed By: alexander-shaposhnikov

Differential Revision: https://reviews.llvm.org/D125833

Author: MaskRay

llvm/lib/ObjCopy/MachO/MachOWriter.cpp

@@ -651,7 +651,6 @@ Error MachOWriter::write() {
     return createStringError(errc::not_enough_memory,
                              "failed to allocate memory buffer of " +
                                  Twine::utohexstr(TotalSize) + " bytes");
-  memset(Buf->getBufferStart(), 0, totalSize());
   writeHeader();
   writeLoadCommands();
   writeSections();