remove redundant updated in favor of modified

First step is removing the overhead of two magic fields doing the same thing.
Will also be closer to the documentation at http://book.cakephp.org/2.0/en/models/saving-your-data.html#using-created-and-modified

As a second step we could then either form a customizable

    public $createdField
    public $modifiedField

attribute for each model (similar to `displayField`), or form it a trait of some kind.

see https://cakephp.lighthouseapp.com/projects/42648/tickets/2870-magic-datetime-fields-should-be-reduced-to-created-and-modified-aliasing