Changelog: Add info about avatar removal

CHANGELOG.md

@@ -16,8 +16,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 <details>
   <summary>API Changes</summary>
 
+- **Breaking:** Pleroma API: The routes to update avatar, banner and background have been removed.
 - **Breaking:** Image description length is limited now.
 - **Breaking:** Emoji API: changed methods and renamed routes.
+- MastodonAPI: Allow removal of avatar, banner and background.
 - Streaming: Repeats of a user's posts will no longer be pushed to the user's stream.
 - Mastodon API: Added `pleroma.metadata.fields_limits` to /api/v1/instance
 - Mastodon API: On deletion, returns the original post text.