Remove opam file warning about upcoming 3.0.0
Remove opam file warning about upcoming 3.0.0

Since the 3.0.0 release is being made right about now.

[skip ci]

ocsigen/lwt,c-cube/lwt,rneswold/lwt,c-cube/lwt,ocsigen/lwt,ocsigen/lwt,c-cube/lwt,rneswold/lwt,rneswold/lwt