message: doc: Remove note about temporary file from release notes
  About time, before tagging final.
  Tree-SHA512:
diff: -## (note: this is a temporary file, to be added-to by anybody, and moved to release-notes at release time)
  -
  Bitcoin Core version 0.16.0 is now available from:
  <https://bitcoincore.org/bin/bitcoin-core-0.16.0/>
  