Removing callbacks in onDetachedFromWindow, fixes b/7465673

In certain cases when lockscreen is constructed in landscape and then
switches to portrait on the phone, it inflates new views for
KeyguardHostView.  The old views never call onPause() in KeyguardFaceUnlockView
so it was still getting callbacks and starting Face Unlock multiple
times.  By removing the callbacks in onDetachedFromWindow() there won't be
multiple instances of KeyguardFaceUnlockView receiving callbacks and
starting face unlock.

Change-Id: I00d770283e83be2f4b76e00340123789a8075091