image_to_usb.sh: This script is deprecated. Replace it with a stub.

BUG=chromium:406132
TEST=Verified with code search that there are no internal callers. Ran
manually and verified that the error message was printed successfully.

Change-Id: I1205af8b009ba9aaa0b5e51b3c55dd3b7293512f
Reviewed-on: https://chromium-review.googlesource.com/213005
Reviewed-by: Gabe Black <gabeblack@chromium.org>
Tested-by: Gabe Black <gabeblack@chromium.org>
Commit-Queue: Gabe Black <gabeblack@chromium.org>
3 files changed