rm changelog for unreleased changes fixes

Based on https://github.com/rails/rails/pull/23167/files#r50507317

[ci skip]

actionpack/CHANGELOG.md

-*   Fix `ActionController::Parameters==`
-
-   *Jon Moss*
-
 *   Response etags to always be weak: Prefixes 'W/' to value returned by
    `ActionDispatch::Http::Cache::Response#etag=`, such that etags set in
    `fresh_when` and `stale?` are weak.