[kcmultidialog] Remove unneeded margins from KPageView
This is as targeted but slightly hacky alternative to kwidgetsaddons!15 (closed).
It removes the margins around the content area that are no longer needed, because KCM content is expected to be able to touch the screen edges. Margins are added to the button box because we don't want them to touch the window edges.
Current appearance:
BUG: 431855 FIXED-IN: 5.80
Edited by Nate Graham