Remove unused queue.stopped_N (#16850)

Marlin/src/gcode/queue.cpp

@@ -52,7 +52,7 @@ GCodeQueue queue;
  * sending commands to Marlin, and lines will be checked for sequentiality.
  * M110 N<int> sets the current line number.
  */
-long gcode_N, GCodeQueue::last_N, GCodeQueue::stopped_N = 0;
+long gcode_N, GCodeQueue::last_N;
 
 /**
  * GCode Command Queue

Marlin/src/gcode/queue.h

@@ -35,9 +35,7 @@ public:
    * commands to Marlin, and lines will be checked for sequentiality.
    * M110 N<int> sets the current line number.
    */
-  static long last_N, stopped_N;
-
-  static inline void stop() { stopped_N = last_N; }
+  static long last_N;
 
   /**
    * GCode Command Queue