Fix WM presubmit failures

Use legacy approach to move activities to split-screen to fix
wm presubmit failures after 8ee6300 landed.

Bug: 177180570
Test: atest ManifestLayoutTests AssistantStackTests
      MultiDisplayPolicyTests PinnedStackTests
Change-Id: I4ceb115b667d50de24f69f1bbf54531e2cb9368c
4 files changed