mail-crypt-acl: Fix logging while updating private keys for shared users

mail-crypt-acl: Fix logging while updating private keys for shared users

During userdb lookup the log prefix contained only the user being looked up
with no mention of the originating user. This was because
mail_storage_service_lookup() didn't see that there was any IO loop context
active, so it created a new log prefix. Fixed by simply removing the
explicit IO loop context [de]activate calls. The logging seems to work just
fine even without them.