Fixing outdated cgal_header_clean_up.py in developer scripts.

[SharonIV0x86]

Issue Details

Fixing outdated cgal_header_clean_up.py script in developer script folder of the project. Here
The current version of the cgal_header_clean_up.py script, which was last updated 14 years ago, is written in an outdated Python version and no longer works properly. It needs to be migrated to Python 3 and fixed to correctly format copyright holder names, placing each name on a separate line. I would like to make this change. If this issue is assigned to me i will make sure that cgal_header_clean_up.py works as intended.

Environment

• Operating system: Linux x64
• Compiler: g++ MinGW
• CGAL version:6.0.1
• Other libraries versions if used (Eigen, TBB, etc.) N/A:

[sloriot]

The script has only been used 14 years ago for updating some files. It is kept for archive.

[SharonIV0x86]

The script has only been used 14 years ago for updating some files. It is kept for archive.

Might be possible that it's required in future someday, wouldn't it be better to update it?