www/py-dj21-django-cors-headers: Update to 2.5.2

While I'm here:

• Make port architecture neutral by adding NO_ARCH

Changelog since 2.4.0:

• Improve inclusion of tests in sdist to ignore .pyc files.
• Include test infrastructure in sdist to allow consumers to use it.
• Drop Django 1.8, 1.9, and 1.10 support. Only Django 1.11+ is supported now.
• Fix DeprecationWarning from importing collections.abc.Sequence on Python3.7.

https://github.com/ottoyiu/django-cors-headers/blob/2.5.2/HISTORY.rst

Approved by: mentors (implicit)