Delete the obsolete code for accessibility title population

For now we could get the window title from ViewRootImpl, so
we delete all obsolete code. Besides we add new string
for the tile of the pip window and split-screen divider

Bug: 210985169
Test: atest android.accessibilityservice.cts
      manual test with talkback
Change-Id: Ia418b2f4175636c2109082b8daeb7b2cc1cfd845