feat: Remove now-unneeded call to seed permissions for demo course forums

[timmc-edx]

This is now redundant with the earlier import call, which at this point goes ahead and does the seeding.

One of these is probably used by sandboxes, and the other is probably not, but both are referenced by ansible-provision.sh. Might as well remove from both so that at least they're consistent with devstack, and so that this is not propagated forward to whatever eventually replaces the sandbox setup scripts.

See openedx-unsupported/devstack#1129 for details.

Configuration Pull Request

Make sure that the following steps are done before merging:

• A SRE team member has approved the PR if it is code shared across multiple services and you don't own all of the services.
• Are you adding any new default values that need to be overridden when this change goes live? If so:
  • Update the appropriate internal repo (be sure to update for all our environments)
  • If you are updating a secure value rather than an internal one, file a SRE ticket with details.
  • Add an entry to the CHANGELOG.
• If you are making a complicated change, have you performed the proper testing specified on the Ops Ansible Testing Checklist? Adding a new variable does not require the full list (although testing on a sandbox is a great idea to ensure it links with your downstream code changes).
• Think about how this change will affect Open edX operators. Have you updated the wiki page for the next Open edX release?

[rgraber]

LGTM