Remove "Citation Software" guide from homepage guides rotation

[djanelle-mit]

Developer

We discovered that the guide for Citation Software was no longer available, and the link is broken. To remedy this we decided to remove the link to that guide from the rotation of expert guides available on the homepage.

This work removes that guide from the group that included it.

Stylesheets

• Any theme or plugin whose stylesheets have changed has had its version
  string incremented.

Secrets

• All new secrets have been added to Pantheon tiers
• Relevant secrets have been updated in Github Actions
• All new secrets documented in README

Documentation

• Project documentation has been updated
• No documentation changes are needed

Accessibility

• ANDI or Wave has been run in accordance to
  our guide and
  all issues introduced by these changes have been resolved or opened as new
  issues (link to those issues in the Pull Request details above)

Stakeholder approval

• Stakeholder approval has been confirmed
• Stakeholder approval is not needed

Dependencies

YES | NO dependencies are updated

Code Reviewer

• The commit message is clear and follows our guidelines
  (not just this pull request message)
• The changes have been verified
• The documentation has been updated or is unnecessary
• New dependencies are appropriate or there were no changes

[matt-bernhardt]

This is a straightforward change, so I don't have any concerns. I don't remember there being any lower limit to the number of guides in a panel.

Ultimately this might be a candidate for re-implementation in a way that allows someone to curate these lists outside of code, but that would be best handled as part of the homepage redesign project, not here.

[djanelle-mit]

@matt-bernhardt Yes, exactly... that might be something we want to add to the scope if we're keeping that section around (some kind of standardized WP object/post/page/etc. for these).