Removing almost all new_untyped_evar, and a bunch of Evd.add.
Ultimately all evars should be created with respect to a given
evar map, instead of using a global counter.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16783 85f007b7-540e-0410-9357-904b9bb8a0f7