Use androidx.test.filters.FlakyTest

Tests previously used a mixed between
- androidx.test.filters.FlakyTest
- android.platform.test.annotations.FlakyTest

Annotations, there's already an ayeaye (g3) analyzer to guide users towards the correct one.

Bug: 311643481
Flag: TEST_ONLY
Test: atest FlickerTests
Change-Id: I7b3be1aefdb57de6a10115ee830fe086cddc05f0