launch: Avoid specifically starting PA and rely on autospawn/socket activation

launch: Avoid specifically starting PA and rely on autospawn/socket activation

This --start is patched out in several downstreams to allow users to easily
disable PA by simply disabling autospawn.

If autospawn is enabled, then the first pactl command will start it and if not
it will fail and the script will exit.

When switching to systemd socket activation, we very much do not want to
start PA manually here. We could replace it with a
  systemctl --user start pulseaudio
but really it just makes sense to rely on the socket activation as this
should apply equally to non-systemd setups which use PA's own autospawn.

Change-Id: Ie730dacd598453f0bd3493cb3df3467a805a7a8b