s/Record Elimination/Nonrecursive Elimination/

As per https://coq.inria.fr/bugs/show_bug.cgi?id=3586, [Set Record
Elimination Schemes] is going away eventually.
Merge pull request #474 from JasonGross/set-nonrecursive-elim

s/Set Record Elimination Schemes/Set Nonrecursive Elimination Schemes/