* 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.