Remove TestExpectations for some no-longer-flaky fullscreen tests

None of these appear to have any recent failures in the flakiness dashboard:
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=full-screen-remove-ancestor.html
http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=full-screen-iframe-allowed.html

To verify, the affected tests were run with --iterations=1000 on Linux
Debug/Release and Mac Debug builds with no failures or timeouts.

BUG=100798
BUG=243782

Review URL: https://codereview.chromium.org/448463002

git-svn-id: svn://svn.chromium.org/blink/trunk@179592 bbb929c8-8fbe-4397-9dbb-9b2b20218538