launchers: remove launchers

Moving forward we're going to be supporting libseat and logind as our
only launchers. We're doing this to reduce our maintenance burden,
and security impact.

Libseat supports all our existing use cases, and seatd can replace
weston-launch so we no longer have to carry a setuid-root program.

This patch removes weston-launch, and launcher-direct, leaving only
libseat and logind.

Signed-off-by: Derek Foreman <derek.foreman@collabora.com>

doc/sphinx/toc/running-weston.rst

@@ -91,17 +91,14 @@ You can start Weston from a VT assuming that there's a seat manager supported by
 backend to be used by ``libseat`` can optionally be selected with
 ``$LIBSEAT_BACKEND``.  If ``libseat`` and ``seatd`` are both installed, but
 ``seatd`` is not already running, it can be started with ``sudo -- seatd -g
-video``.  If no seat manager supported by ``libseat`` is available, you can use
-the ``weston-launch`` application that can handle VT switching.
+video``.
 
 Another way of launching Weston is via ssh or a serial terminal.  The simplest
 option here is to use the ``libseat`` launcher with ``seatd``.  The process for
 setting that up is identical to the one described above, where one just need to
 ensure that ``seatd`` is running with the appropriate arguments, after which one
 can just run ``weston``.  Another option, is to rely on logind and start weston
-as systemd user service: :ref:`weston-user-service`. Alternatively and as a last
-resort, one can run Weston as root, specifying the tty to use on the command
-line: If TTY 2 is active, one would run ``weston --tty 2`` as root.
+as systemd user service: :ref:`weston-user-service`.
 
 Running Weston on a different seat on a stand-alone back-end
 ------------------------------------------------------------