Revert "Maintain change log file directly on trunk branch in push-to-trunk." and related changes.

This reverts r19876, r19902 and r19903. The changes made git diff' in push-to-trunk unusable.

TBR=jarin@chromium.org

Review URL: https://codereview.chromium.org/197313005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19905 ce2b1a6d-e550-0410-aec6-3dcde31c8c00