Fix misplaced EditFilterHook return value documentation

This return value documentation was added to hooks.txt in May 2006
(f064b66c64) for EditFilter. In December 2007 (0693d79fb6) the
sections were reordered, incorrectly placing this text in the
EditPage::showEditForm:initial section. This error was carried forward
to the present.

Change-Id: I49c01ebfada493a42ef520984e77b4deffd52d34