Remove "Status Whiteboard", "External issue ID", and possibly "External URL" from the Create Issue options

The dialog is confusing enough to users unfamiliar with it. We don't need unnecessary fields.
The External fields are just for BZ compat, so shouldn't be set in new issues (unless the description for the URL field is wrong, and it's also for download URLs and such). And even I don't know what Status Whiteboard is for.