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/freestyle/intern/python/UnaryFunction0D/BPy_UnaryFunction0DVectorViewShape.h

@@ -18,8 +18,7 @@
  * \ingroup freestyle
  */
 
-#ifndef __FREESTYLE_PYTHON_UNARYFUNCTION0DVECTORVIEWSHAPE_H__
-#define __FREESTYLE_PYTHON_UNARYFUNCTION0DVECTORVIEWSHAPE_H__
+#pragma once
 
 #include "../BPy_UnaryFunction0D.h"
 
@@ -53,5 +52,3 @@ int UnaryFunction0DVectorViewShape_Init(PyObject *module);
 #ifdef __cplusplus
 }
 #endif
-
-#endif /* __FREESTYLE_PYTHON_UNARYFUNCTION0DVECTORVIEWSHAPE_H__ */