The main visible effect of this is that if console-conf crashes or is killed
it restarts instantly rather than 90 seconds later. It also removes the flicker
where a getty gets started and then instantly killed during startup.
* debian/console-conf.*.serial: Start the console-conf wrappers from
their path in /usr/share/subiquity; no need to have them in /usr/bin.
* bin/console-conf-serial-wrapper: add --serial to the command-line.
* debian/console-conf.serial-console-conf@.service: don't pass --serial,
this is meant to be parameters to agetty, not to the login program.