Apparently some instances have local users with local ap_ids
that are marked as local: false. Needs more investigation into how
that happened.
In the meantime, the skeleton migration was patched to just ignore
all known ap ids, not just locals. Doesn't seem to slow down the migration
too much on patch.cx
Closes#1746
Prevents the possibility of re-registration, which allowed to read
DMs of the deleted account.
Also includes a migration that tries to find any already deleted
accounts and insert skeletons for them.
Closespleroma/pleroma#1687