COPYING.LIB: Synchronize the LGPL 2.1 with the version from gnu.org

COPYING.LIB: Synchronize the LGPL 2.1 with the version from gnu.org

The current version of the LGPL 2.1 from gnu.org (see the URL
https://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt ) slightly
differs from the old one that we use in our repository. Especially
the recommendation to use "either version 2 of the License, or [...]
any later version" is somewhat misleading, since there was never a
"version 2" of the "Lesser GPL" license - the "version 2" was still
called "Library GPL" instead.

Signed-off-by: Thomas Huth <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>
Message-Id: <1548252536[email protected]>
Signed-off-by: Laurent Vivier <[email protected]>