Add SPDX short license identifier to all Python files

See: https://spdx.github.io/spdx-spec/appendix-V-using-SPDX-short-identifiers-in-source-files/

dspace_statistics_api/indexer.py

@@ -1,23 +1,7 @@
+# SPDX-License-Identifier: GPL-3.0-only
 #
 # indexer.py
 #
-# Copyright 2018 Alan Orth.
-#
-# This program is free software: you can redistribute it and/or modify
-# it under the terms of the GNU General Public License as published by
-# the Free Software Foundation, either version 3 of the License, or
-# (at your option) any later version.
-#
-# This program 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 General Public License for more details.
-#
-# You should have received a copy of the GNU General Public License
-# along with this program.  If not, see <http://www.gnu.org/licenses/>.
-#
-# ---
-#
 # Connects to a DSpace Solr statistics core and ingests views and downloads for
 # communities, collections, and items into a PostgreSQL database.
 #