Prevents Activate and Register pages from showing in the Pages meta box of the Menu Administration screen.

In the same way these pages are not displayed on the page listings, they will be hidden from the available items of the Pages meta box in the menus administration. This also avoids confusion with the register item of BuddyPress dynamic links.

Fixes #5323

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7741 cdf35c40-ae34-48e0-9cc9-0c9da1808c22