ui.rc files: consistenly use <gui> instead of deprecated <kpartgui>

gui/ksysguardui.rc

-<!DOCTYPE kpartgui>
-<kpartgui name="ksysguard" version="5">
+<?xml version="1.0"?>
+<!DOCTYPE gui SYSTEM "kpartgui.dtd">
+<gui name="ksysguard" version="5">
 <MenuBar>
   <Menu name="file"><text>&amp;File</text>
     <Action name="new_worksheet"/>
@@ -28,5 +29,5 @@
     <Separator/>
     <Action name="configure_sheet"/>
 </ToolBar>
-</kpartgui>
+</gui>