Merge AppWindowTokenTests into ActivityRecordTests

AppWindowTokenTests is actually the same as ActivityRecordTests, so
merge them into one.

Also remove @FlakyTest since they have been passing for over 1 month on
the dashboard.

Bug: 144248496
Bug: 131005232
Bug: 131176283
Test: atest ActivityRecordTests
Change-Id: I6e06f09268181f4653897d86d4477a27576b8c5d