Remove factory_test from build_image target types.

The 'factory_test' image has been deprecated by toolkit for a long time.
To unify the build process and make documentation easier, we want to
deprecate the factory_test output type so people will always use factory
toolkit.

BUG=chromium:577601
TEST=build_image; build_image test; build_image factory_install

Change-Id: I81af7abb05ea71b4babf28f32674e621b3fa50aa
Reviewed-on: https://chromium-review.googlesource.com/348170
Commit-Ready: Hung-Te Lin <hungte@chromium.org>
Tested-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Shun-Hsing Ou <shunhsingou@chromium.org>
Reviewed-by: Wei-Ning Huang <wnhuang@chromium.org>
5 files changed