Stop recognizing FTP addresses
I'm not sure if Epiphany can handle FTP, if I type such an address it opens up in a Firefox tab for me.
This means it'll be pointless for us to recognize this protocol anymore (and also to set $FTP_PROXY). Even if the user clicked on it, it wouldn't open up properly in the browser.
Let's remove this from GNOME 3.38, or 3.40 the latest. (What's up with ftps and sftp? Can we drop those, too? I guess so.)