Revert "[DWARF][BOLT] Implement new mechanism for DWARFRewriter"

This reverts commit 460a224.
It breaks building on macOS, and it was landed with a review URL
pointing to some Facebook-internal service.

Also reverts a bunch of follow-ups:

Revert "[BOLT][DWARF] Don't check string offsets"
This reverts commit f9d6f48.

Revert "[BOLT][DWARF] Change to process and write out TUs first then CUs in batches"
This reverts commit 88e95c1.

Revert "[BOLT][DWARF] Output DWO files as they are being processed"
This reverts commit 46ca2e3.

Revert "[BOLT][DWARF] Don't check string offsets"
This reverts commit cfe4a4b.

Revert "[BOLT][DWARF] Numerous fixes for a new DWARFRewriter"
This reverts commit 2701a66.

Author: nico