Revert "Make URLs case sensitive"

This actually doesn't help for two reasons:

• the Rake task is broken, as both filenames are the same
• Netlify doesn't like mixed-case names https://www.jvt.me/posts/2019/11/11/gotcha-netlify-lowercase/

This should've been done at the time of jamietanna/www-api!31 (merged), but wasn't.

This reverts commit b82db8dc.