Merge "Don't show back arrow in Security when in split mode." into tm-dev am: e22fa138aa am: a474c51a04 am: d6c1353a80

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/apps/Settings/+/17940206

Change-Id: Ic6e6d1654463ef13c352eb3b959f1593077a790b
Ignore-AOSP-First: this is an automerge
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>