This reverts commit ebe6e3180e.
This is wrong, as mutter's controlling TTY may not be the same
as the active VT, and in fact won't be in the case of systemd
spawning us.
The "correct" API for this is to use David Herrmann's
"Session Positions" system to switch to another VT:
http://lists.freedesktop.org/archives/systemd-devel/2013-December/014956.html
Now that we have a setuid launcher binary, we can make use of
using a private protocol through the socket we're passed at startup.
We also use the new hook in clutter-evdev to ask mutter-launch for
the FDs of the input devices we need, and we emulate the old X
DRM lock with a nested GMainContext without sources.
In the future, mutter-launch will be replaced with the new logind
API currently in development.
https://bugzilla.gnome.org/show_bug.cgi?id=705861
