Fix kill => disable_all_heaters => print_job_timer.stop (#12146)

- Remove `print_job_timer.stop()` from `disable_all_heaters`
- Call `print_job_timer.stop()` for relevant `disable_all_heaters()`.
- Split up `kill()` for watchdog interrupt safety

Marlin/src/lcd/malyanlcd.cpp

@@ -254,9 +254,7 @@ void process_lcd_p_command(const char* command) {
         quickstop_stepper();
         print_job_timer.stop();
         thermalManager.disable_all_heaters();
-        #if FAN_COUNT > 0
-          for (uint8_t i = 0; i < FAN_COUNT; i++) fan_speed[i] = 0;
-        #endif
+        zero_fan_speeds();
         wait_for_heatup = false;
         write_to_lcd_P(PSTR("{SYS:STARTED}"));
       #endif

Marlin/src/lcd/ultralcd.cpp

@@ -1918,9 +1918,7 @@ void lcd_quick_feedback(const bool clear_buttons) {
   #endif // HAS_TEMP_HOTEND || HAS_HEATED_BED
 
   void lcd_cooldown() {
-    #if FAN_COUNT > 0
-      for (uint8_t i = 0; i < FAN_COUNT; i++) fan_speed[i] = 0;
-    #endif
+    zero_fan_speeds();
     thermalManager.disable_all_heaters();
     lcd_return_to_status();
   }