brillo_update_payload: Drop common.sh.

This releases us from pulling in unnecessary dependencies, which is
useful in some situations (like running this script in a Moblab image):

1) Source shflags directly. Look at the default location, then crosutils
   (chroot), then the current directory (for au-generator.zip).

2) Define a die function locally.

BUG=b:24909273
TEST=Script runs in Moblab.

Change-Id: Id4c8764ee20635b4822fa71b3719690a46c44f4a
Reviewed-on: https://chromium-review.googlesource.com/305759
Commit-Ready: Gilad Arnold <garnold@chromium.org>
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed