Fix form submission on Special:RandomInCategory

You can't have parameters in the action for GET forms, browsers are
going to trim them off.

This is the way passing title in handled on other special pages,
e.g. Special:Contributions.

Change-Id: I00728a085641b8a6cda50a55ad1e9b1de68b97bc
Merge "Fix form submission on Special:RandomInCategory"