Case light brightness cleanup (#19856)

Co-authored-by: Chris <chris@chrisnovoa.com>

Marlin/src/lcd/extui/ui_api.cpp

@@ -610,7 +610,7 @@ namespace ExtUI {
       caselight.update_enabled();
     }
 
-    #if DISABLED(CASE_LIGHT_NO_BRIGHTNESS)
+    #if CASELIGHT_USES_BRIGHTNESS
       float getCaseLightBrightness_percent()                 { return ui8_to_percent(caselight.brightness); }
       void setCaseLightBrightness_percent(const float value) {
          caselight.brightness = map(constrain(value, 0, 100), 0, 100, 0, 255);