Cleanup: remove redundant, invalid info from headers

BF-admins agree to remove header information that isn't useful,
to reduce noise.

- BEGIN/END license blocks

  Developers should add non license comments as separate comment blocks.
  No need for separator text.

- Contributors

  This is often invalid, outdated or misleading
  especially when splitting files.

  It's more useful to git-blame to find out who has developed the code.

See P901 for script to perform these edits.

source/blender/blenlib/BLI_math.h

@@ -1,6 +1,4 @@
 /*
- * ***** BEGIN GPL LICENSE BLOCK *****
- *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
  * as published by the Free Software Foundation; either version 2
@@ -20,7 +18,6 @@
  *
  * The Original Code is: some of this file.
  *
- * ***** END GPL LICENSE BLOCK *****
  * */
 
 #ifndef __BLI_MATH_H__