Optimize and audit static images

[lukekarrys]

• Images in static/ are only used up to certain widths. They can be bulk resized so the source matches this width. See https://www.gatsbyjs.com/docs/preoptimizing-images/
• Some images are no longer used. They are copied directly from the static/ dir so we need to make sure they are not expected at those paths from anywhere outside this repo.

[chris-bateman]

Hey @lukekarrys I see #748 covered the resizing. Did you still need someone to audit the images that are no longer used?