Remove unused requirements-devel.txt

requirements-devel.txt

-# -*- coding: utf-8 -*-
-#
-# Copyright (C) 2020 - 2021 TU Wien.
-#
-# Invenio-Utilities-TUW is free software; you can redistribute it and/or
-# modify it under the terms of the MIT License; see LICENSE file for more
-# details.
-#
-# TODO: Add development versions of some important dependencies here to get a
-#       warning when there are breaking upstream changes, e.g.:
-#
-#     -e git+git://github.com/mitsuhiko/werkzeug.git#egg=Werkzeug
-#     -e git+git://github.com/mitsuhiko/jinja2.git#egg=Jinja2