Disable unimplemented PID_ADD_EXTRUSION_RATE

Firmware/Configuration_adv.h

@@ -13,7 +13,7 @@
 #ifdef PIDTEMP
   // this adds an experimental additional term to the heating power, proportional to the extrusion speed.
   // if Kc is chosen well, the additional required power due to increased melting should be compensated.
-  #define PID_ADD_EXTRUSION_RATE
+  // #define PID_ADD_EXTRUSION_RATE
   #ifdef PID_ADD_EXTRUSION_RATE
     #define  DEFAULT_Kc (1) //heating power=Kc*(e_speed)
   #endif

Firmware/temperature.h

@@ -23,9 +23,8 @@
 
 #include "Marlin.h"
 #include "planner.h"
-#ifdef PID_ADD_EXTRUSION_RATE
-  #include "stepper.h"
-#endif
+
+#include "stepper.h"
 
 #include "config.h"
 
@@ -91,7 +90,10 @@ extern bool bedPWMDisabled;
 
 #ifdef PIDTEMP
   extern int pid_cycle, pid_number_of_cycles;
-  extern float Kc,_Kp,_Ki,_Kd;
+  extern float _Kp,_Ki,_Kd;
+#ifdef PID_ADD_EXTRUSION_RATE
+  extern float Kc;
+#endif
   extern bool pid_tuning_finished;
   float scalePID_i(float i);
   float scalePID_d(float d);