Update SHARED-FILES and license for Unicode 15.1.0.

In 2018 the license changed to use Unicode-3.0 license.
The Unicode License is a permissive MIT type of license.
Automation is updated to fetch the correct license file to
keep it in sync with the data files.

The new license is OSI approved and has an SPDX identifer:
https://opensource.org/license/unicode-license-v3
https://spdx.org/licenses/Unicode-3.0.html

The FSF and the GNU Project have been contacted to update
the license list for this license:
https://www.gnu.org/licenses/license-list.html