Fix behaviour of destruct after change of case representation.
Fix behaviour of destruct after change of case representation.

We ensure not to generate dummy beta-cuts in case branches generated
by destruct. There was seemingly code trying to perform this but in
an akward way.

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