Remove redundant MockitoJUnit.rule()

MockitoAnnotations.initMock() has been introduced as a part of
I06c8162d4196, but redundant MockitoJUnit.rule() accidentally slipped
through being removed.

Bug: 113800711
Test: atest WmTests:com.android.server.wm.SurfaceAnimationRunnerTest
Change-Id: I861e1fb6f54db561e58f0a58cb2c3768a0556b89
1 file changed