Remove legacy activity transition animation callback

The callback methods are only used by legacy transition, which are
no longer used.

The operation of DisplayContent#onWindowAnimationFinished is replaced
by Transition#finishTransition -> removeImeSurfaceImmediately.

Bug: 365884835
Flag: EXEMPT remove unused code
Test: CtsWindowManagerDeviceWindow
Change-Id: I5742d5e257b2a0edb1dd9ec7e2ca497dec94bf34