Apply #pragma once, misc cleanup (#12322)

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

Marlin/src/module/stepper.h

@@ -19,6 +19,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  *
  */
+#pragma once
 
 /**
  * stepper.h - stepper motor driver: executes motion plans of planner.c using the stepper motors
@@ -40,9 +41,6 @@
  * along with Grbl.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef STEPPER_H
-#define STEPPER_H
-
 #include "../inc/MarlinConfig.h"
 
 // Disable multiple steps per ISR
@@ -559,5 +557,3 @@ class Stepper {
 };
 
 extern Stepper stepper;
-
-#endif // STEPPER_H