Revert "Port async delivery methods to Rails 3"

This reverts commit 328c1d73eff901180a6a677f1edd36f1212c7774.
Port async delivery methods to Rails 3

Original code by Jean-Philippe Lang
redmine:b590ff105e2e69ccd5b06c2783860e78bc1b392b

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extra : rebase_source : fe089df7bb9dd7a7983b841aed65ffb5f612c261