Fix wait_for_user compile error (#13352)

Marlin/src/feature/emergency_parser.h

@@ -31,10 +31,7 @@
   #include "host_actions.h"
 #endif
 
-// External references
-extern volatile bool wait_for_user, wait_for_heatup;
-void quickstop_stepper();
-void host_response_handler(const uint8_t response);
+#include "../Marlin.h"
 
 class EmergencyParser {