Make many gnus version variables obsolete

Make many gnus version variables obsolete

Many haven't been bumped since 1997, others not since 2004.
* lisp/gnus/deuglify.el (gnus-outlook-deuglify-version):
* lisp/gnus/gnus-diary.el (gnus-diary-version):
* lisp/gnus/nnagent.el (nnagent-version):
* lisp/gnus/nnbabyl.el (nnbabyl-version):
* lisp/gnus/nndiary.el (nndiary-version):
* lisp/gnus/nndir.el (nndir-version):
* lisp/gnus/nndoc.el (nndoc-version):
* lisp/gnus/nndraft.el (nndraft-version):
* lisp/gnus/nneething.el (nneething-version):
* lisp/gnus/nnfolder.el (nnfolder-version):
* lisp/gnus/nnmaildir.el (nnmaildir-version):
* lisp/gnus/nnmbox.el (nnmbox-version):
* lisp/gnus/nnmh.el (nnmh-version):
* lisp/gnus/nnml.el (nnml-version):
* lisp/gnus/nnrss.el (nnrss-version):
* lisp/gnus/nnspool.el (nnspool-version):
* lisp/gnus/nntp.el (nntp-version):
* lisp/gnus/nnvirtual.el (nnvirtual-version): Make obsolete in
favor of emacs-version.