[BD-21] Get rid of deprecated waffle namespace classes

[regisb]

The WaffleSwitchNamespace class is going to be deprecated soon.
edx-platform needs this app to stop using the namespace class in order
to upgrade to the latest edx-toggles release.

JIRA: https://openedx.atlassian.net/wiki/spaces/COMM/pages/1596358943/BD-21+Toggles+Settings+Documentation

Reviewers:

• @robrap

Merge checklist:

• All reviewers approved
• CI build is green
• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Commits are squashed

Post merge:

• Create a tag
• Check new version is pushed to PyPi after tag-triggered build is
  finished.
• Delete working branch (if not needed anymore)

Note that this will break unit tests in edx-platform.

[openedx-webhooks]

Thanks for the pull request, @regisb! I've created BLENDED-653 to keep track of it in Jira. More details are on the BD-21 project page.

When this pull request is ready, tag your edX technical lead.

[regisb]

This is ready for review @robrap.

[robrap]

Reminder to update dependencies once it has been released. I will update the PR description as well.

[robrap]

Is there any advantage to making this work with the __futures__ version so it isn't blocked on edx-toggles 2.0.0 to complete, or do you want to leave this blocked until edx-toggles 2.0.0?

[regisb]

Is there any advantage to making this work with the futures version so it isn't blocked on edx-toggles 2.0.0 to complete, or do you want to leave this blocked until edx-toggles 2.0.0?

Good question. It would make it easier to run CI on this PR, as we would only have to wait for the the release of edx-toggles==1.2.0. But we should not release this too early; otherwise, if people need to make changes to edx-completion, they would also need to upgrade edx-platform and the applications (if any) that make use of the deprecated waffle() function.

[robrap]

Another option is leaving this, setting a deprecated custom attribute, and making this v3.2.6 instead of v4.0.0 with no backward compatible changes. That way, if we missed anything where this was used outside of tests, we could catch it before its removal.

[regisb]

If this breaks anything then the fix should be relatively straightforward. edx-platform should not be impacted, so we should only be concerned by other applications. I think this is a reasonable risk.

[regisb]

@robrap Can we merge this now that edx-toggles has been upgraded to 1.2.0 on edx-platform?

[robrap]

This can merge after the minor changelog fix.

[regisb]

@robrap done 👍