Debian: clean up copyright file

We were drawing a dep5-copyright-license-name-not-unique lintian
warning. I've eliminated the duplicate Apache-2.0 text, combining
the sections. Furthermore, I've relicensed the Debian files
under Apache-2.0 mainly to reduce complexity.

debian/copyright

@@ -5,23 +5,11 @@ Source: https://nick-black.com/dankwiki/index.php/notcurses
 Files: *
 Copyright: 2019-2020 Nick Black <dankamongmen@gmail.com>
 License: Apache-2.0
- Licensed under the Apache License, Version 2.0 (the "License");
- you may not use this file except in compliance with the License.
- You may obtain a copy of the License at
- .
- https://www.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,
- WITHnot WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- See the License for the specific language governing permissions and
- limitations under the License.
- .
- On Debian systems, the complete text of the Apache version 2.0 license
- can be found in "/usr/share/common-licenses/Apache-2.0".
 
 Files: src/libcpp/* include/ncpp/*
 Copyright: 2019-2020 Marek Habersack <grendel@twistedcode.net>
+License: Apache-2.0
+
 License: Apache-2.0
  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
@@ -37,22 +25,3 @@ License: Apache-2.0
  .
  On Debian systems, the complete text of the Apache version 2.0 license
  can be found in "/usr/share/common-licenses/Apache-2.0".
-
-Files: debian/*
-Copyright: 2019-2020 Nick Black <dankamongmen@gmail.com>
-License: GPL-2+
- This package 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 2 of the License, or
- (at your option) any later version.
- .
- This package is distributed in the hope that it will be useful,
- but WITHnot ANY WARRANTY; withnot 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 <https://www.gnu.org/licenses/>
- .
- On Debian systems, the complete text of the GNU General
- Public License version 2 can be found in "/usr/share/common-licenses/GPL-2".