copyright: Simplify notices (automatic part)

copyright: Simplify notices (automatic part)

Remove dates and list of authors from most file headings.

  $ cat >b
   * userv is copyright Ian Jackson and other contributors.
   * See README for full authorship information.
  $ cat >a
   * userv is
   * Copyright 1996-2017 Ian Jackson <ian@davenant.greenend.org.uk>.
   * Copyright 2000      Ben Harris <bjh21@cam.ac.uk>
   * Copyright 2016-2017 Peter Benie <pjb1008@cam.ac.uk>
  $ git-grep -l 'Copyright 1996-2017 Ian Jackson' | A=$(cat a) B=$(cat b) xargs perl -i~ -pe 'BEGIN { $/=undef; }; s/\Q$ENV{A}\E/$ENV{B}/'
  $

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>