Drop supplementary groups for child zygotes. am: 7c8779c0 am: 80cfa981 am: 75f35b04 am: 69db3557

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/11691614

Change-Id: I1b500f5594402797c6c34040832c747382066f88