doc: Clear out release notes post-0.16.0
doc: Clear out release notes post-0.16.0

Moved to: https://github.com/bitcoin/bitcoin/blob/master/doc/release-notes/release-notes-0.16.0.md

Tree-SHA512: 6619521357a1baa5df2d4deb9e75784f6f48711a7b5d5120cf02b47a80e242e41dcf34dadfd1b257bbdcd883c7dd216d36fbfff24abcf03c590bbf0f6bbec520

Conflicts:
	doc/release-notes.md

chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin,chaincoin/chaincoin