When executing tests for Edge, UI events are processed on teardown of
the test (or more precisely on widget disposal) as there may still be
resources related to the OS WebView component being cleaned up. The
current implementation was only supposed to be used for testing purposes
as an attempt to address non-deterministic timeouts in tests. However,
the timeouts still occur and the current implementation is prone to
break as it may never terminate when new events to be process arrive
frequently.

This change simplifies the cleanup functionality to process UI events
only once instead of looping it. This mitigates the risk of a
long-running loop and reduces unnecessary complexity.