Omit CMS and 21W courses in favor of CMS-W

[pdpinch]

In the raw JSON export from plone, we have discovered multiple courses with the same slug. For an example, see mitodl/ocw-to-hugo#470

After consulting with the OCW team, I learned that we don't need to import courses from the legacy CMS and 21W departments, because they were all moved into CMS-W.

I suspect that when we have slug collisions, it's unpredictable which one we will import. We should be omitting any courses in the CMS or 21W directories.

Acceptance Criteria:

• [x] Do some research to confirm the nature and scope of the problem
• [ ] build a list of courses that would need to be re-imported. How many of them would be new arrivals in ocw-studio produciton, like the one mentioned in mitodl/ocw-to-hugo#470?
• [ ] If a re-import will overwrite courses in production, we will need a strategy for preserving course author changes (or get permission to ignore them)

Related issues

• There may be similar issues with the ESD department, but I'd like to do some more investigation.

[pdpinch]

I've reviewed about half of the 21W and CMS courses in production studio, and so far everything is from the preferred CMS-W version.

[pdpinch]

Is this still necessary, do you think?

[pdpinch]

This is moot