Single user mode basically disables WebDAV, OCS and cron execution. Since
we heavily rely on WebDAV and OCS also in the web UI it's basically useless.
An admin only sees a broken interface and can't even change any settings nor
sees any files. Also sharing is not possible.

As this is at least the case since Nextcloud 9 and we haven't received any
reports for this it seems that this feature is not used at all so I removed it.

The encryption commands now rely on the well tested maintenance mode.

Signed-off-by: Morris Jobke <hey@morrisjobke.de>