Mark .pyf interface definition as CC0

It is likely uncopyrightable.

src/fortran/wignerSymbols.pyf

 !    -*- f90 -*-
 
-! Copyright (c) Christopher Kerr 2018
+! SPDX-FileCopyrightText: 2018 Christopher Kerr
 !
-! This file is part of GALUMPH.
-!
-! GALUMPH is free software: you can redistribute it and/or modify it
-! under the terms of the GNU Lesser General Public License as published
-! by the Free Software Foundation, either version 3 of the License, or
-! (at your option) any later version.
-!
-! GALUMPH is distributed in the hope that it will be useful,
-! but WITHOUT ANY WARRANTY; without even the implied warranty of
-! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-! GNU Lesser General Public License for more details.
-!
-! You should have received a copy of the GNU Lesser General Public License
-! along with GALUMPH.  If not, see <http://www.gnu.org/licenses/>.
+! SPDX-License-Identifier: CC0-1.0
 
 python module wignerSymbols
     interface