Update changelog format and content

Removed changelog header and added design token note.

Author: B3nz01d

components/ai_assistant/assistant_button/dsm/changelog.md

@@ -1,5 +1,3 @@
-# Changelog
-
 | Date | Number | Notes | Designer |
 |------|--------|-------|----------|
-| Jun 8, 2026 | 1.0.0 | Version 2.6 of the design tokens is required for the development of this update.<ul><li>Component creation</ul> | Maxime Tonnerre |
+| Jun 8, 2026 | 1.0.0 | Version 2.6 of the design tokens is required for the development of this update.<ul><li>Component creation</ul> | Maxime Tonnerre |