landingpage: Fix broken binding in "Most Used Pages" grid

First rule of the fighting club: never bind to a list. You never know
what the heck you're up against.

On the other hand, assigning FormData.buddyFor in a procedural way in
the Repeater's hook is robust, and there's nothing that could go wrong.

CCBUG: 468712
(cherry picked from commit 3bc36d5f)