Remove window obscurement information.

If ACTION_OUTSIDE_EVENTS contain information about whether the touch is
obscured, then a pattern of invisible, untouchable, unfocusable
SYSTEM_ALERT_WINDOWS can be placed across the screen to determine
approximate locations of touch events without the user knowing.

Bug: 31097064
Test: cts-tradefed run cts --class android.security.cts.MotionEventTest
Merged-In: Ie30dcc2402d5422a19a43ffe7d1411d91681efc2
Change-Id: I1dc5f003ada7ad3c753e078a8c1fbe10a89fb42f