Link to changelog from README

[MarkEWaite]

Link to changelog from README

Document that new releases and several older releases are documented in the GitHub release page instead of using the changelog file.

Remove obsolete files.

Testing done

Confirmed that automated tests pass.

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests - that demonstrates feature works or fixes the issue