Rename Samba's DCO to Samba Developer's Declaration

Rename Samba's DCO to Samba Developer's Declaration

In an effort to reduce any confusion about the differences
between the Samba DCO and the Linux DCO, and as a favor to the
Linux community, rename the Samba DCO to the Samba Developer's
Declaration.

Signed-off-by: Bradley M. Kuhn <bkuhn@sfconservancy.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Simo Sorce <idra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Tue Oct 20 22:54:01 UTC 2020 on sn-devel-184