Declaremods: drop some useless stuff (slight gain in vo size)

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16406 85f007b7-540e-0410-9357-904b9bb8a0f7
Minor simplifications in Declaremods and Safe_typing

 - get_module_substobjs (resp. modtype) without useless mp_from arg
 - no need for the whole Safe_typing.pack_module
 - ...

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@16407 85f007b7-540e-0410-9357-904b9bb8a0f7