Add changelog entry for killing the asset tag concatenation

actionpack/CHANGELOG.md

 ## Rails 4.0.0 (unreleased) ##
 
+*   Remove old asset tag concatenation (no longer needed now that we have the asset pipeline). *Josh Peek*
+
 *   Accept :remote as symbolic option for `link_to` helper. *Riley Lynch*
 
 *   Warn when the `:locals` option is passed to `assert_template` outside of a view test case