bin/delete-device.php script to delete devices

Either by deviceid/owner or with a time filter (useful to just delete
all devices that haven't connected for a while). Please note that while
this will clear out the syncroton state, it will not clean up the IMAP
annoatations, which will result in the devices being recreated when the
roundcube settings page is openend.

Given that IMAP becomes more complex because of authentication and the
primary purpose for now is to remove legacy data from the database, this
is good enough for now.