Revert "More fixes to get good error messages for bad archives."

Revert "More fixes to get good error messages for bad archives."

This reverts commit r277540. It breaks the build with:

../lib/Object/Archive.cpp:264:41: error: return type of out-of-line definition of 'llvm::object::ArchiveMemberHeader::getUID' differs from that in the declaration
Expected<unsigned> ArchiveMemberHeader::getUID() const {
~~~~~~~~~~~~~~~~~~                      ^
include/llvm/Object/Archive.h:53:12: note: previous declaration is here
  unsigned getUID() const;
  ~~~~~~~~ ^

llvm-svn: 277627