1/ Remove unused legacy recents paths

- We no longer support the legacy recents animation cancel path
  (it was already a no-op)
- Use the shell recents transition path instead of the legacy recents
  animation for remaining use cases

Flag: EXEMPT cleaning up unused code
Bug: 359608026
Test: Test both kb shortcut and desktop split invocation paths
Change-Id: I2726d52b3b4f3533afc4286b155c71eadcb57909