Revert "[DebugInfo][RemoveDIs] Add prototype storage classes for "new" debug-info"

And some intervening fixups. There are two remaining problems:
 * A memory leak via https://lab.llvm.org/buildbot/#/builders/236/builds/7120/steps/10/logs/stdio
 * A performance slowdown with -g where I'm not completely sure what the cause it

These might be fairly straightforwards to fix, but it's the end of the day
hear, so I figure I'll clear the buildbots til tomorrow.

This reverts commit 7d77bbef.
This reverts commit 9026f35a.
This reverts commit d97b2b38.