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

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

Change-Id: Ica692daa7426b5b58126b29dd9f8c71f7ee84272
Ignore-AOSP-First: this is an automerge
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>