Modify test cases for takeScreenshot() API

1. Remove old test cases for testing the API,
takeScreenshot(), due to the return type of the
method, takeScreenshot(), at the AccessibilityService
class, isn't the Bitmap.
2. Add new test cases to test all payloads of
ScreenshotResult are correct.

Bug: 10931661 and 148169867 and 148171895
Test: atest AccessibilityTakeScreenshotTest
Change-Id: Ic1fc5a9fe46ccb0c72557b8d1e2d1b3192bf8dff