Fixes #20939 - stop enabling the openscap repo

[ares]

We already ship our packages and we no longer support el6. We could drop the param completely, but I suppose that'd break class API.

[theforeman-bot]

@ares, the Redmine ticket used is for a different project than the one associated with this GitHub repository. Please either:

• check #20939: Custom repo for openscap is enabled by default for rhel6
  is the correct one
• move ticket #20939 from Foreman to the Installer project
• or file a new ticket in the Installer project

If changing the ticket number used, remember to update the PR title and the commit message (using git commit --amend).

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This message was auto-generated by Foreman's prprocessor

[ekohl]

We should create an issue to remove this for the next major. There's the admin param issue as well.

[ekohl]

Thanks!