Add dummy Emergancy Pin to Gen7 1.4

Change required after pulling from ErikZalm.

Marlin/pins.h

 #define HEATER_2_PIN -1
 #define HEATER_BED_PIN 3
 
+#define KILL_PIN -1
 
 #define SDPOWER -1
 #define SDSS -1 // SCL pin of I2C header