Expurgating the useless difference between List0 and List1 at the
level of generic arguments. This only matters at parsing time.

TODO: the current status is not satisfactory enough, as rule
emptyness is still decided w.r.t. generic arguments. This should be
done on a grammar entry basis instead.

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16617 85f007b7-540e-0410-9357-904b9bb8a0f7