update_payload: Remove ctypes dependency.

ctypes requires libffi.so to be installed in the system, but old
test_images don't have it, preventing "cros flash" to work there.
This patch removes the need for ctypes from common.py so cros flash
can work.

TEST=cros flash from R29 on link.

Change-Id: Idd0732660780081c26375a5214167b53f625e3ed
Reviewed-on: https://chromium-review.googlesource.com/277070
Trybot-Ready: Alex Deymo <deymo@chromium.org>
Tested-by: Alex Deymo <deymo@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Alex Deymo <deymo@chromium.org>
1 file changed