Clear OWNERS for factory/firmware branch

BUG=none
TEST=none

Change-Id: I0f03f432ada1064ffba9595be78ca7ab4d25ecd1
Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3154569
Reviewed-by: Jack Rosenthal <jrosenth@chromium.org>
Owners-Override: Jora Jacobi <jora@google.com>
Tested-by: Jack Rosenthal <jrosenth@chromium.org>