Removal of slug meta box prevents slug changes

[nacin]

The changes in [19444] (#19292) seem to require that the slug metabox remains registered for the page. This is typically the first thing to be de-registered when someone is trying to clean up the boxes on this admin page. We need to make this JS independent of that input box.

Steps to reproduce:

1. Add this code to a mu-plugin:

   add_action( 'add_meta_boxes', function() {
   	remove_meta_box('slugdiv', get_current_screen(), 'normal');
   } );
   

2. Create a post or page. Save.

3. Attempt to change the slug via the live edit. Save.

4. Notice that the slug did not change.

[nacin]

Wait a second, confirmed on 3.2.1. Very odd. I'd think I would have seen a bug report for this one before.

[nacin]

Apparently there was one report: #18523.