login: effectively revert "open device if needed"

login: effectively revert "open device if needed"

This replaces commit 4d3900f1b7ccce03366f9a57d259d0735c1cfbcf.
The underlying cause of issue #8291 has been fixed, so there is no reason
to paper over it any more.

But it might still be useful not to crash in the face of bad restart data.
That can cause several restarts, or maybe at some point an infinite loop
of restarts.  Fail the start (or stop!) request, and write an error to the
system log.  Each time reflects a user request where we fail to resume the
display server's access (or revoke it), and it can be useful if the log
shows the most recent one.