Streamline and fix code header notice

[pombredanne]

• The current notice can be simplified like in ScanCode toolkit and DejaCode.
• It is missing copyright entirely

Instead of https://github.com/nexB/scancode.io/blob/4e274f09996a21c427a42fedc7e99920a76d9ce9/scanpipe/management/commands/add-input.py#L1C1-L21C70

# SPDX-License-Identifier: Apache-2.0
#
# http://nexb.com and https://github.com/nexB/scancode.io
# The ScanCode.io software is licensed under the Apache License version 2.0.
# Data generated with ScanCode.io is provided as-is without warranties.
# ScanCode is a trademark of nexB Inc.
#
# You may not use this software except in compliance with the License.
# You may obtain a copy of the License at: http://apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software distributed
# under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
# CONDITIONS OF ANY KIND, either express or implied. See the License for the
# specific language governing permissions and limitations under the License.
#
# Data Generated with ScanCode.io is provided on an "AS IS" BASIS, WITHOUT WARRANTIES
# OR CONDITIONS OF ANY KIND, either express or implied. No content created from
# ScanCode.io should be considered or used as legal advice. Consult an Attorney
# for any legal advice.
#
# ScanCode.io is a free software code scanning tool from nexB Inc. and others.
# Visit https://github.com/nexB/scancode.io for support and download.

We should use this:

#
# Copyright (c) nexB Inc. and others. All rights reserved.
# ScanCode is a trademark of nexB Inc.
# SPDX-License-Identifier: Apache-2.0
# See https://github.com/nexB/scancode.io for support or download.
# See https://aboutcode.org for more information about AboutCode FOSS projects.
#