default Model onRemove(ModelTransformer transformer, Collection<Shape> removed, Model model) {
        return model;
    }
The method that is invoked each time shapes are removed from a model.

@param transformer Transformer used to replace/remove shapes from the model.
@param removed The of shapes that were removed from the {@code model}.
@param model Model that has been altered to remove {@code removed}.
@return Returns a transformed version of the passed in model.
smithy-model/src/main/java/software/amazon/smithy/model/transform/ModelTransformerPlugin.java