Remove `snk` mode

.. it is likely this is not needed.
Actually causes some boards to outright fail.

Remove it for now / add to subset of boards as needed.
(which hopefully will never be the case)

Followup will be to remove select src mode transitions, but can keep
for now to leave minimal changes.

BUG=b:400555073
TEST=CQ + (need to wait for rollout)

Change-Id: I8f391db91db8295972d8dd69831c9b1f8e2a803f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/6320773
Commit-Queue: Derek Beckett <dbeckett@chromium.org>
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Auto-Submit: Jae Hoon Kim <kimjae@chromium.org>
Reviewed-by: Derek Beckett <dbeckett@chromium.org>
Commit-Queue: Jae Hoon Kim <kimjae@chromium.org>
1 file changed