Conditionally omit edition numbers, dates in doc

Conditionally omit edition numbers, dates in doc

This redoes the 2019-11-02T00:24:02!eggert@cs.ucla.edu patch,
updated after consultation with John Sullivan.
Omit printed edition numbers in online manuals while keeping
them in printed manuals.  In online manuals the edition
numbers seem to cause more confusion than they cure; e.g.,
https://shop.fsf.org/books/gnu-emacs-manual-18th-edition-v-261
currently advertises "18th edition" even as it points to
https://www.gnu.org/software/emacs/manual/pdf/emacs.pdf which
says "Seventeenth Edition".  It is simpler and less confusing
to stick to one version number like "27.0" in online manuals.
For printed manuals people can run, e.g., "texi2any -D
'EDITION Nineteenth'" when generating the 19th printed edition
of the Emacs manual.
* doc/emacs/emacs.texi (EDITION):
* doc/lispintro/emacs-lisp-intro.texi (edition-number, update-date):
* doc/lispref/elisp.texi (VERSION, DATE):
Remove definitions.  Instead, let the person printing the book
specify these values, with the default being the online version
which does not have printed edition numbers.
* doc/lispintro/emacs-lisp-intro.texi (titlepage-edition-number):
New flag, for the edition number as it appears on the title page.