Code Style: use "#pragma once" in source directory

This replaces header include guards with `#pragma once`.
A couple of include guards are not removed yet (e.g. `__RNA_TYPES_H__`),
because they are used in other places.

This patch has been generated by P1561 followed by `make format`.

Differential Revision: https://developer.blender.org/D8466

source/blender/nodes/NOD_common.h

@@ -21,8 +21,7 @@
  * \ingroup nodes
  */
 
-#ifndef __NOD_COMMON_H__
-#define __NOD_COMMON_H__
+#pragma once
 
 #include "BKE_node.h"
 
@@ -49,5 +48,3 @@ void node_group_output_update(struct bNodeTree *ntree, struct bNode *node);
 #ifdef __cplusplus
 }
 #endif
-
-#endif /* __NOD_COMMON_H__ */