[#31675] Remove last uses of JRequest in Joomla

Combined with #3677 this should remove all instances of JRequest from Joomla - which paves the way for it's removal in J4.0 :D

http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=31675

JRequest filtered by CMD by default. So I presume we should with JInput as well?