OWNERS: add alanstokes, remove nnk am: 3aea2bd6ac am: 2b20a67476 am: 5dcb287181 am: b975bafc29

Original change: https://android-review.googlesource.com/c/platform/external/selinux/+/1704948

Change-Id: Ie593052400b206332c8db3dbb67f0b88047fe14d