ANDROID: Remove all but top-level OWNERS

Now that the branch is used to create production GKI
images, need to institute ACK DrNo for all commits.

The DrNo approvers are in the android-mainline branch
at /OWNERS_DrNo.

Bug: 240999246
Signed-off-by: Todd Kjos <tkjos@google.com>
Change-Id: Id5bb83d7add5f314df6816c1c51b4bf2d8018e79