Events: applyFilters() supports only callbacks for all arguments

See [this line](https://github.com/Automattic/o2/blob/9a8be6b17fbfe4c4cb55ac88597020d89279057d/js/utils/events.js#L138): If a filter provides two arguments but your callback needs only the first one the callback doesn't get called.

Start at applyFilters() in js/utils/events.js around line 138 and reproduce the case where a filter supplies two arguments but the callback accepts only the first. Done means the callback is invoked with the usable arguments in that case, while existing filter behavior remains unchanged.

Written by the indexing model from the issue text.