Merge "Don't show back arrow in Security when in split mode." into tm-dev am: e22fa138aa am: 2a9fb8aa47 am: cfd80d65f0 am: 1e9e82e937

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

Change-Id: Ib39351a67daafb3c690555b4629e852c5c6366d5
Ignore-AOSP-First: this is an automerge
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>