Fix compiler warning: sketch/Marlin_main.cpp:8759:8: warning: unused variable 'c' [-Wunused-variable]

Firmware/Marlin_main.cpp

@@ -8756,7 +8756,6 @@ void restore_print_from_eeprom() {
 	int feedrate_rec;
 	uint8_t fan_speed_rec;
 	char cmd[30];
-	char* c;
 	char filename[13];
 	uint8_t depth = 0;
 	char dir_name[9];