CHANGELOG: remove duplicated top header (#20)

Author: ada4a

CHANGELOG.md

@@ -16,13 +16,6 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 * incomplete documentation for sink and interner
 
-# Changelog - imara-diff
-
-All notable changes to imara-diff will be documented in this file.
-The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
-and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
-
-
 ## 0.1.7 - 2024-26-7
 
 ### Fixed