deleting a bundle doesn't remove it from the $field data

Here's a simple way to see this:

1. Enable forum module
2. Create a content type, say 'forum two'.
3. Add the forum vocab field to it.
4. Observe that at /forum you get two node creation links, one for each content type that may appear in the forum
5. Delete the content type!
6. Return to /forum. The second link is still there, but now missing the content type name.

The $field array returned by field_info_field() still has the deleted content type in $field['bundles']['node'].