During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
This was the last untyped handler from the HomeServer object. Since
it was being treated as Any (and thus unchecked) it was being used
incorrectly in a few places.
By always using delete_devices and sometimes passing a list
with a single device ID.
Previously these methods had gotten out of sync with each
other and it seems there's little benefit to the single-device
variant.
