Remove unused callback consumer in TaskOrganizerController

The mDeferTaskOrgCallbacksConsumer becomes a dead code since [1]
that changes to call TOC#dispatchPendingEvents directly from
RootWindowContainer and WindowAnimator.

[1]: Ic8fea93117f45b60f15b06773eefbbde11e48fd5

Bug: 163976519
Test: WindowOrganizerTests
Change-Id: I7ec2c534fcce0c97862a92b162dee0d303dd6032
3 files changed