FIX: Drop the yyyy-mm-dd placeholder from the Unreleased changelog header so PVP-40-1 passes

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: jfreire-unity

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -5,7 +5,7 @@ All notable changes to the input system package will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
-## [Unreleased] - yyyy-mm-dd
+## [Unreleased]
 
 ### Fixed