Apply #pragma once, misc cleanup (#12322)

* Apply #pragma once in headers
* Adjust some thermistors formatting
* Misc cleanup and formatting

Marlin/src/HAL/HAL_DUE/MarlinSerialUSB_Due.h

@@ -19,15 +19,13 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * MarlinSerialUSB_Due.h - Hardware Serial over USB (CDC) library for Arduino DUE
  * Copyright (c) 2017 Eduardo José Tagle. All right reserved
  */
 
-#ifndef MARLINSERIALUSB_DUE_H
-#define MARLINSERIALUSB_DUE_H
-
 #include "../../inc/MarlinConfig.h"
 
 #if SERIAL_PORT == -1
@@ -92,4 +90,3 @@ private:
 extern MarlinSerialUSB customizedSerial1;
 
 #endif // SERIAL_PORT == -1
-#endif // MARLINSERIAL_DUE_H