drupalSettings are never removed after AJAX request

For me, this throws errors if you have multiple ajax calls on the page. I'm providing an alternative that only clears out facets once they're sent to the autocomplete function, so that you don't get errors about autocomplete_settings[data_id] being empty.

It turned out our code was depending on the "default_value" of each facet to display a "clear" button and apply a class, so here's a version of the last patch that preserves that value per-facet, along with an interdiff between comment 4&5.