Delete unused rules from wiki-screen.css

Usage was tested both in source code and in wiki content. Content that
used a rule infrequently or unnecessarily was updated so that the rule
could be removed.
Remove the forum-archive landing page

In the last year, the page garnered only 13 pageviews.
Merge pull request #2199 from openjck/remove-forum-archive

Remove the forum-archive landing page
Merge pull request #2198 from openjck/delete-unused-wiki-screen-rules

Delete unused rules from wiki-screen.css