Ensure Bubbles get removed at the end of the test

- Fix an NPE found when removing bubbles at the end of the test
- Remove all the bubbles at the end of the test
- Remove the @Flaky annotation

Bug: 259961387
Test: run the tests in gradle and check the ahprof file
Change-Id: Ic7eff0c3cd1dd78c25c9e80479134f2e0ce2cbd7