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/blenlib/BLI_scanfill.h

@@ -17,8 +17,7 @@
  * All rights reserved.
  */
 
-#ifndef __BLI_SCANFILL_H__
-#define __BLI_SCANFILL_H__
+#pragma once
 
 /** \file
  * \ingroup bli
@@ -131,5 +130,3 @@ bool BLI_scanfill_calc_self_isect(ScanFillContext *sf_ctx,
 #ifdef __cplusplus
 }
 #endif
-
-#endif