Revert "meta-weston-launch: Call VT_ACTIVATE ourselves"

This reverts commit ebe6e3180ed842445c5145c6947aae9c3fa270a5.

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