The MathML CG agrees to drop it from MathML Core, it duplicates the <msqrt> element and is not used in practice: https://github.com/mathml-refresh/mathml/issues/3#issuecomment-475507647
We don't support radical: https://searchfox.org/wubkat/source/Source/WebCore/mathml/MathMLMencloseElement.cpp#62 So nothing to do here.