Removing legacy transitions calls in window organizer

- Pre-shell transit Split was the last user of legacy transitions, and
  that was cleaned up recently so we can remove the legacy call as well

Bug: 365884835
Bug: 378565144
Flag: EXEMPT removing unused code
Test: Build fw/sysui
Change-Id: I5987d865555063f129c5ade2799e9800c43cef39