Review taxonomy/term listings and disable those of low value (SEO)

[jenlampton]

We should review and disable our taxonomy/term pages, and disable those that are not valuable to the site. Having lots of pages on a site that offer little value can hurt a site's ranking in search results, as the value is split across all pages. A site with fewer high-quality pages will rank higher than one with a lot of low-value pages.

Pages worth reviewing:

• https://backdropcms.org/services/e-commerce
• TBD

This is a follow-up to #913