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

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

Change-Id: I2abb93f9a2673f7acb628951bd2218417cbaebd7