doc: consolidate & remove release-note fragments

These have been moved here:
https://github.com/bitcoin-core/bitcoin-devwiki/wiki/24.0-Release-Notes-draft.

Author: fanquake

doc/README.md

@@ -53,7 +53,6 @@ The Bitcoin repo's [root README](/README.md) contains relevant information on th
 
 - [Developer Notes](developer-notes.md)
 - [Productivity Notes](productivity.md)
-- [Release Notes](release-notes.md)
 - [Release Process](release-process.md)
 - [Source Code Documentation (External Link)](https://doxygen.bitcoincore.org/)
 - [Translation Process](translation_process.md)