Merge "Clean up the legacy split screen (6/n)" into tm-dev am: fafcf3c4 am: bba5028d

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/base/+/16962007

Change-Id: I6ff6d3a1dc6a7bc73e773824fa61b8cde3978c76