Revert "DebugInfo: Temporarily work around -gsplit-dwarf + LTO...

Revert "DebugInfo: Temporarily work around -gsplit-dwarf + LTO .debug_gnu_pubnames regression after D94976"

Backing out this workaround to focus on fixing whatever's wrong with
.debug_gnu_pubnames, I'll revert the cause, (8998f584) in the next commit.

This reverts commit 56fa34ae.