mathml_element: remove unused variable.
mathml_element: remove unused variable.

janmarthedal/mathml2svg,wavewave/lasem,janmarthedal/mathml2svg,gjtorikian/lasem,gjtorikian/lasem,wavewave/lasem,gjtorikian/lasem,wavewave/lasem,gjtorikian/lasem,janmarthedal/mathml2svg,janmarthedal/mathml2svg,wavewave/lasem