Clean up UI declarations, apply TERN_

Marlin/src/MarlinCore.h

@@ -38,19 +38,9 @@
 
 void stop();
 
-void idle(
-  #if ENABLED(ADVANCED_PAUSE_FEATURE)
-    bool no_stepper_sleep=false    // Pass true to keep steppers from timing out
-  #endif
-);
-
-inline void idle_no_sleep() {
-  idle(
-    #if ENABLED(ADVANCED_PAUSE_FEATURE)
-      true
-    #endif
-  );
-}
+// Pass true to keep steppers from timing out
+void idle(TERN_(ADVANCED_PAUSE_FEATURE, bool no_stepper_sleep=false));
+inline void idle_no_sleep() { idle(TERN_(ADVANCED_PAUSE_FEATURE, true)); }
 
 #if ENABLED(EXPERIMENTAL_I2CBUS)
   #include "feature/twibus.h"