devserver: stop importing cros_update

We already execute it as a standalone program in one codepath, so
do that all the time.  This simplifies the code too, and allows us
to migrate cros_update to Python 3 before devserver.

BUG=chromium:1057760
TEST=CQ passes

Change-Id: Ia8ac2db5e053c783b7ddf8ae4ddfb65a3484d6c5
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2083676
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
1 file changed