Call show_search_field_default after a result is selected.

@harvesthq/chosen-developers 

#1701 is kind of a non-issue in my eyes, but the change is simple enough and I actually prefer this to what exists now. After selecting a result, we should always be resetting a field's value the same way. This adds an extra class removal call in the non-multiple version, but it's harmless.

What say you?

Fixes #1701