Refactor configuring RemoteFactoryGirl implementation

This refactor is a simpler implementation and uses less code.

* In RemoteFactoryGirl.configure block, instead of converting the block
to an OpenStruct and pass the OpenStruct hash in to Config, use `yield`
in RemoteFactoryGirl.configure.
* Removes ‘virtus’ gem, no need for type checking. The type checking
worked when the value was set initially.