Do not allocate AConstr evar instances.
Do not allocate AConstr evar instances.

They are never used by [w_unify_to_subterm], and it should save a lot
of memory in fiat-crypto.

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