Deprecate `ActionController::RecordIdentifier`.

This module was moved on the `ActionView` extraction, but 3rd party gems [like webrat](https://github.com/brynary/webrat/blob/master/lib/webrat/adapters/rails.rb#L2-L6) are including the `RecordIdentifier` module on its own and they will break on the 4.0 -> 4.1 upgrade. 

There might be more modules out there that might be worth adding the deprecation too - let me know and we can deprecate everything under the same commit/PR.

/cc @strzalek @carlosantoniodasilva @rafaelfranca