Remove unused function switchUnitsInMathML.
Remove unused function switchUnitsInMathML.

cellml/libcellml,hsorby/libcellml,cellml/libcellml,nickerso/libcellml,nickerso/libcellml,nickerso/libcellml,MichaelClerx/libcellml,MichaelClerx/libcellml,cellml/libcellml,nickerso/libcellml,hsorby/libcellml,hsorby/libcellml,cellml/libcellml,MichaelClerx/libcellml,hsorby/libcellml