Do not update mocked environment by real display events

The real display listener is registered in
RootWindowContainer#setWindowManager.

Some test may set up display size in @Before, but when running
the real test method, the display size of the mocked display is
updated by real display info.

e.g. according to WindowManagerGlobalLockRule:
  1. test thread: lockWm {@Before}
  2. ui thread: lockWm {onDisplayChanged} <- flaky race
  3. test thread: lockWm {test method}

Fix: 309542567
Test: atest DisplayPolicyLayoutTests#testSimulateLayoutDisplay
Change-Id: I2b00a09b14497573d4b09873351aac73f56e70eb