public Model removeUnreferencedShapes(Model model) {
        return removeUnreferencedShapes(model, FunctionalUtils.alwaysTrue());
    }
Removes shapes (excluding service shapes) that are not referenced by
any other shapes.

@param model Model to transform.
@return Returns the transformed model.base.
smithy-model/src/main/java/software/amazon/smithy/model/transform/ModelTransformer.java