Revert "Use summary message on non Main namespace pages"

The 'summary' message is full wikitext, can't be used properly from JS.

This reverts commit c806942a3403144770f4036787aad000142098a6.

Change-Id: Ie27bbd10e51a89340f502fa4cd6d0f7ca4683c3c
(cherry picked from commit bea4a0c5964deb6b20f5500459c6c6cb732b2c02)