Fixes to Special:PagesWithProp

- Remove unneeded call to HTMLForm::setAction()
- Call HTMLForm::setWrapperLegendMsg() instead of HTMLForm::setWrapperLegend()
- Use Html::element() instead of Xml::span()

Change-Id: I4bc90c223a89bd31ce2d93a959e9bdf4b546e6dd
Merge "Fixes to Special:PagesWithProp"