Validate or remove import-from-course-to-content-library feature

[kdmccormick]

https://github.com/openedx/edx-platform/blob/master/openedx/core/djangoapps/content_libraries/management/commands/content_libraries_import.py

This was added in an earlier blockstore-based implementation of V2 libraries. We haven't tested it in a while, so we need to either test and fix it up, or remove it.

Additionally, some known issues, while it was still on blockstore:

• migration command quietly fails to create bundleversion under tutor dev with async celery
• in migration command, LibraryAlreadyExists error prints out V1 key instead of V2 key