Okay, but that this is not needed is not true. Because especially if you do not use HSTS HTTPS Everywhere still protects against SSL stripping.
HSTS is basically just a HTTP header. And if I understand it correctly OpenLiteSpeed also uses Apache config files and there are many guides how to add a (HSTS) header in Apache. Also for only serving it via HTTPS (which is recommend anyway, because HSTS headers served over HTTP are ignored by clients anyway).
Although TLS is indeed fast, especially if you also support HTTP/2 like you do I understand that you may not want to serve your releases over HTTPS by default.
As for HTTPS Everywhere users they'll get them over HTTPS (as they use this extension, it seems useful). The purpose of serving binaries over HTTPS is simple: Integrity. Because HTTPS does not only prevent eavesdropping on the traffic, but also makes sure the integrity of the packages is guaranteed. This means with HTTPS an attacker cannot modify the binary.
So I would at least recommend to put the hash (SHA-1 and preferable SHA-256) on the (HTTPS) download site, so that the user can verify the (HTTP) download manually.
I just rescanned and it is still there:
E.g. in this thread there is this smiley:
http://www.wildfiregames.com/forum/uploads//emoticons/default_smile.png
It seems that all smileys inserted before the forum relaunch are still HTTP links...
BTW on this page there is another mixed content: The social media icons, e.g.:
http://www.wildfiregames.com/0ad/images/new_icons/facebook.png
are served over HTTP.
FYI if you cannot rewrite all links or it is to difficult there is a "workaround" by using the CSP header.
It does not really matter. All the smileys are the default, old forum-smileys...
But I can live with them...