Remove kde3 compatibility code for "DocPath" in desktop files

LXR suggests nothing still sets that (everything is X-DocPath now).

REVIEW: 117003

src/core/kdesktopfile.cpp

@@ -330,10 +330,6 @@ KDesktopFile::sortOrder() const
 QString KDesktopFile::readDocPath() const
 {
     Q_D(const KDesktopFile);
-    //legacy entry in kde3 apps
-    if (d->desktopGroup.hasKey("DocPath")) {
-        return d->desktopGroup.readPathEntry("DocPath", QString());
-    }
     return d->desktopGroup.readPathEntry("X-DocPath", QString());
 }