clean up the mess, the nuke-room-from-db.sh script did

[rubo77]

The old nuke-room-from-db.sh script from synapse master (before it was removed) did not delete all traces of a room, so I tried to clean up the remaindants with these commands: https://github.com/matrix-org/synapse/pull/3888#issuecomment-429538928

But I am not sure, if these are safe to use. maybe you can have a look, please?