Always go via PAM for autologin

This passes our session through the systemd PAM module that sets up
logind correctly, fixing a bug where polkit actions would not work
correctly in an SDDM session
Provide seat name and virtual terminal number to PAM environment variables
remove pointless pam checks in autologin
Merge pull request #142 from davidedmundson/fix_autologin

Fix Polkit sessions with autologin