api/Caddyfile.prod: remove experimental_http3 and use default for protocols section
api/Caddyfile.prod: remove experimental_http3 and use default for protocols section

Also use default for whole server section.
This seems to be disabled in the new caddy version.
Now the protocol section accepts space separated values of:
h1 h2 h2c h3
Default is h1 h2 h3
See: https://caddyserver.com/docs/caddyfile/options#protocols

The .prod file forgotten in f8d05ca

ecamp/ecamp3,ecamp/ecamp3,ecamp/ecamp3,usu/ecamp3,usu/ecamp3,ecamp/ecamp3,usu/ecamp3,usu/ecamp3