public static String stripQuotes(String s) {
        if (isNotQuoteSign(s.codePointAt(0))) return s;
        if (isNotQuoteSign(s.codePointAt(s.length() - 1)))
            throw new IllegalArgumentException("argument [" + s + "] is missing end quote");
        return s.substring(1, s.length()-1);
    }
Transforms ONNX model features of the forms:

    onnx(config_name)
    onnx(config_name).output
    onnx("path/to/model")
    onnx("path/to/model").output
    onnx("path/to/model", "path/to/output")
    onnx("path/to/model", "unused", "path/to/output")    // signature is unused

To the format expected by the backend:

    onnx(config_name).output

@author lesters
config-model/src/main/java/com/yahoo/schema/expressiontransforms/OnnxModelTransformer.java