Many of the relations had missing symbol tags, and many relations with symbol tags pointed to PNG thumbnails rather than the source SVG on Wikimedia Commons. I think I got all of them pointed to the SVGs. I also upgraded URLs to https since it was likewise an even mix of http/https.

This one's probably less important for data consumers than the MO E issue (which was problematic for OpenStreetMap Americana), but I wanted it to be consistent as well.