django52: remove deprecated DEFAULT_FILE_STORAGE and STATICFILES_STORAGE.

[awais786]

django.core.files.storage.get_storage_class is deprecated in favor of using django.core.files.storage.storages.

Similar PRs created inside edx-platform and course-discovery but no one yet merged.

For reference.

openedx/edx-platform#37002

[sumair-arbisoft]

I am working on this one.