Sanitize calling sites of wDefaultsCheckDomains()

There is no point in having parameter in wDefaultsCheckDomains() and
not using it, so let's simply remove the parameter altogether and
avoid silly-looking things like

    wDefaultsCheckDomains("bla");

src/defaults.h

@@ -46,7 +46,7 @@ void wDefaultUpdateIcons(WScreen *scr);
 
 void wReadStaticDefaults(WMPropList *dict);
 
-void wDefaultsCheckDomains(void *screen);
+void wDefaultsCheckDomains(void);
 
 void wSaveDefaults(WScreen *scr);