use gnulib's update-copyright script to update copyright years

use gnulib's update-copyright script to update copyright years

This patch now retires the old copyright.sh script which was using
emacs to perform the copyright update. It also completely rewrite
copyright.py to call update-copyright with the appropriate list
of files.

In addition to calling update-copyright, the new script also performs
a sanity-check on all the files that update-copyright could not update,
and sees whether the file might contain a copyright notice that
the script could not decipher.

gdb/ChangeLog:

        * copyright.sh: Delete.
        * copyright.py: Rewrite.