Desktop -> Split: Don't set windowing mode changes on the wcts.

For historical reasons, we used to set windowing mode changes as we
start these transitions and even on animation callbacks. However now we
don't need them anymore, and setting them actually causes some issue as
now pre-split-select tasks are getting forwarded to no TaskListeners
since we don't have any TaskListeners for Multi Window type windows.
Similarly explicitly setting UNDEFINED to the task after the
split-select animation finishes is unnecessary, given it never changed
windowing mode.

Bug: 410838192
Test: Check for DMWindowDecor callbacks for layout, see a visibility change callback now when drag-to-split-select
Flag: com.android.window.flags.enable_input_layer_transition_fix
Change-Id: I6bbbc79578b6a4df3f3b31806ca1daff7bab0c17