Disabled vocabularies should not appear as sidebar facets

[dheles]

Describe the bug When a subject vocabulary is disabled, it still gets a "Browse subject tree" link in the sidebar subject facet.

To Reproduce Steps to reproduce the behavior:

1. Configure your repository to disable the default srsc vocabulary with the following setting: webui.browse.vocabularies.disabled = srsc
2. keep the default enabled: false value here: https://github.com/DSpace/dspace-angular/blob/bfeeeac96f52b6eddab360778a5f22e84693db70/src/config/default-app-config.ts#L485
3. (Re)deploy your DSpace
4. Observe that the Browse By Subject Category no longer appears in the top navigation dropdown
5. Complete a search and open the "Subject" facet
6. Observe that there is still a "Browse subject tree" link, which when clicked will open a modal using the disabled vocabulary

Expected behavior When a vocabulary is disabled, there should not be a link to use it as a search facet. If no vocabularies are enabled, there should be no "Browse subject tree" link at all.

Related work Original PR for the feature: #1988

[dheles]

A couple of screenshots documenting the issue: