how to undefine class in ruby?
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undefining method in ruby is pretty simple we can just use `undef METHOD_NAME`, I was wondering is there anything similar for `class` in ruby? I am on `MRI 1.9.2`. 
My use case is I have to undefine an `ActiveRecord Model` run 2 lines of code and store back model to its original form.

The problem is I have an model `Contact` and I am using some companies api and it happens that they have some class called `Contact` changing my model name would be lot of work for me. What can I do in this situation?