Remove dead user-facing code in scheme generation.
Remove dead user-facing code in scheme generation.

It was trying to warn the user about missing schemes. Since find_scheme was
generating those constants anyways, this was never reached.

Zimmi48/coq,Zimmi48/coq,ejgallego/coq,JasonGross/coq,JasonGross/coq,coq/coq,ejgallego/coq,gares/coq,Zimmi48/coq,gares/coq,JasonGross/coq,silene/coq,silene/coq,coq/coq,gares/coq,coq/coq,SkySkimmer/coq,coq/coq,SkySkimmer/coq,gares/coq,Zimmi48/coq,SkySkimmer/coq,SkySkimmer/coq,gares/coq,silene/coq,JasonGross/coq,ejgallego/coq,ejgallego/coq