Adapts MotionEvent test to observe touch events while touchexploration is on.

Also removes FlakyTest annotation; per our test dashboard these tests
are not flaky.

Bug: 344604959
Flag: com.android.server.accessibility.always_allow_observing_touch_events
Test: atest AccessibilityEndToEndTest
Change-Id: I4ff9ea48fbd567f2a9149008547439b839fd76b1