Use ActivityLaunchUtils to launch activities in UiAutomationTest.

The 3 tests in this class which launch an activity are ~5% flaky
which recently seems to be from leftover system dialogs from
other tests. ActivityLaunchUtils has more robust activity-launching
logic that goes to the home screen first and closes popups before
launching the activity, which has proven more reliable.

(Also removes unused UiAutomationTestSecondActivity)

Bug: 270722665
Bug: 270752780
Test: atest UiAutomationTest
Test: Used go/abtd to run 50x: http://go/abtd-run/L50700000960459736
Change-Id: Ib0cb75c4fc89318f341c63156254526e478b6cd8
5 files changed