Plugins: Reduce number of CSS classes in blocks

[pkevan]

While this issue existed before the update, we should reduce the amount of CSS classes that are put into elements on the page, particularly if they aren't used.

See example below on a card with many committers, support reps and contributors.

plugins/

They appear due to querying plugin taxonomies associated with the post type, so we could filter them out where appropriate. It seems that plugin_contributors, plugin_committers, plugin_support_reps could be removed, but unsure.