[mach-o] remove __compact_unwind atoms once __unwind_info has been generated

The job of the CompactUnwind pass is to turn __compact_unwind data (and
__eh_frame) into the compressed final form in __unwind_info. After it's done,
the original atoms are no longer relevant and should be deleted (they cause
problems during actual execution, quite apart from the fact that they're not
needed).

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@221301 91177308-0d34-0410-b5e6-96231b3b80d8
[PECOFF] Fix symbols in module-definition file.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@221303 91177308-0d34-0410-b5e6-96231b3b80d8