TouchExplorer: remove dependency on AccessibilityGestureDetector#firstTapDetected.

Since we have proper states now this only serves as extra coupling to the gesture detector.
Bug: 136131815
Test: atest CtsAccessibilityTestCases  CtsAccessibilityServiceTestCases
Test: atest FrameworksServicesTests:TouchExplorerTest
Change-Id: I3be0f05e6492abad6a79f5167aaa61325dc5e9e6