message: add copyright, remove irc channel
diff: Format: http://www.debian.org/doc/packaging-manuals/copyright-format/1.0/
  Upstream-Name: BitcoinUnlimited
  Upstream-Contact: Andrew Stone <g.andrew.stone@gmail.com>
  - irc://#bitcoin@freenode.net
  -Source: https://github.com/bitcoin/bitcoin
  +Source: https://github.com/BitcoinUnlimited/BitcoinUnlimited
  Files: *
  -Copyright: 2009-2016, Bitcoin Developers
  +Copyright: 2009, Satoshi Nakamoto
  + 2009-2016, Bitcoin Core Developers
  + 2015-2019, The Bitcoin Unlimited developers
  License: Expat
  Comment: The Bitcoin Developers encompasses the current developers listed on bitcoin.org,
  on www.bitcoinunlimited.info and numerous other contributors to the project.
  