org-manual: Shorten author field

* doc/org-manual.org (Export Setup): Shorten author field, which was
  larger than the width of the page, and not fair to all the people
  involved in the manual.

doc/org-manual.org

@@ -20776,8 +20776,7 @@ modify this GNU manual."
 * Export Setup                                                          :noexport:
 
 #+subtitle:  Release {{{version}}}
-#+author:    by Carsten Dominik
-#+subauthor: with contributions by Bastien Guerry, Nicolas Goaziou, Eric Schulte, Jambunathan K, Dan Davison, Thomas Dye, David O'Toole, and Philip Rooke.
+#+author:    The Org Mode Developers
 #+date:      {{{modification-time}}}
 #+language:  en