Declare some <package>-version variables obsolete

Declare some <package>-version variables obsolete

These are not used for anything these days and can therefore be
removed.  Package developers should check the Emacs version instead.
Ref: https://lists.gnu.org/r/emacs-devel/2020-03/msg00080.html

* lisp/calendar/icalendar.el (icalendar-version):
* lisp/dframe.el (dframe-version):
* lisp/emacs-lisp/checkdoc.el (checkdoc-version):
* lisp/emulation/edt.el (edt-version):
* lisp/international/mule.el (mule-version)
(mule-version-date):
* lisp/linum.el (linum-version):
* lisp/play/bubbles.el (bubbles-version):
* lisp/speedbar.el (speedbar-version):
* lisp/textmodes/remember.el (remember-version):
* lisp/url/url-vars.el (url-version):
* lisp/woman.el (woman-version): Declare obsolete.

* lisp/emacs-lisp/checkdoc.el (checkdoc-start-section):
* lisp/speedbar.el (speedbar-mode):
* lisp/url/url-about.el (url-about-protocols):
* lisp/url/url-http.el (url-http--user-agent-default-string):
* lisp/url/url-news.el (url-news-fetch-message-id):
* lisp/woman.el (woman-menu, woman-mode): Stop using variables
declared obsolete above.