fuchsia.sys2.EventSource is scheduled for deletion, but is blocked on its inclusion here: https://cs.opensource.google/flutter/engine/+/master:shell/platform/fuchsia/flutter/tests/integration/text-input/meta/text-input-test.cml?

The capability doesn't seem to be used by the test and may be safely removed.