drop support for X

We aren't using X anywhere in the system anymore, so drop all the
scripts/logic that only works with it.

BUG=chromium:842060
TEST=precq passes

Change-Id: I63b591fa0daf190e43b3d749377bffdcad8789d3
Reviewed-on: https://chromium-review.googlesource.com/1055307
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Chung-yih Wang <cywang@chromium.org>