[RuntimeDyld] Revert r211652 - MachO object GDB registration support.

The registration scheme used in r211652 violated the read-only contract of
MemoryBuffer. This caused crashes in llvm-rtdyld where macho objects were backed
by read-only mmap'd memory.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213086 91177308-0d34-0410-b5e6-96231b3b80d8