Fixes #7138,BZ1030537 - Prevent file repos being added to views

Looks like we already have the UI covered:

https://github.com/Katello/katello/blob/master/engines/bastion/app/assets/javascripts/bastion/content-views/details/content-view-available-repositories.controller.js#L40

This prevents users from adding file repos to a content view via CLI or API.