style: Clean out unused selectors
loginManager: Kill ConsoleKit support

The code path is completely unmaintained and untested (and probably
unused as well, considering that nobody has complained about accessing
the session object's Active property which does not exist in the
ConsoleKit case).
Most of our ConsoleKit code is already a dummy anyway, just do the
same for the remaining functionality.

https://bugzilla.gnome.org/show_bug.cgi?id=686626