VFS-License-clarification: minor improvements aligning w/ GPLv3 text

VFS-License-clarification: minor improvements aligning w/ GPLv3 text

The phrase "derived work" and word "derived" don't appear in GPLv3;
instead, GPLv3 uses the phrases "modified version" and "based on" to
implement the strong copyleft clause.  Herein, align the VFS
statement with the phrases as they appear in the GPLv3 since Samba's
license is GPLv3-or-later.

Included are also a few other very minor wording changes as suggested
by legal counsel who is experienced with presenting these sorts of
licensing statements to company lawyers and suggests these changes
will comfort that constituency.

Finally, update both occurrences of the statement in the codebase in
two different files.

Signed-off-by: Bradley M. Kuhn <bkuhn@sfconservancy.org>
Reviewed-by: Jim McDonough <jmcd@samba.org>
Reviewed-by: Karolin Seeger <kseeger@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>