Bench: don't print messages from opam uninstall
Bench: don't print messages from opam uninstall

It mostly spams "nothing to do" and is generally useless.

coq/coq,Zimmi48/coq,SkySkimmer/coq,SkySkimmer/coq,ejgallego/coq,SkySkimmer/coq,ejgallego/coq,Zimmi48/coq,coq/coq,coq/coq,ejgallego/coq,coq/coq,SkySkimmer/coq,Zimmi48/coq,Zimmi48/coq,ejgallego/coq