sites: remove sites with broken links and update repository tags

[tmorrell]

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Description

Remove sites with broken links identified in #204. I've done an additional check and haven't been able to identify replacements.

I also changed all the "repository" tags to "institutional-repository", since that's what's actually used with the Repository facet https://github.com/inveniosoftware/inveniosoftware.org/blob/7be488af582efebce98ce09cf50c6beeaabc8a97/templates/menu.html

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
• I've added relevant documentation.
• I've marked translation strings.
• I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
• I've NOT included third-party code (copy/pasted source code or new dependencies).
  • If you have added third-party code (copy/pasted or new dependencies), please reach out to an architect.

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