Reduce some unnecessary function calls of 'calculateSymmetryNumber'

Some CPU time profiling shows implementation of function 'calculateSymmetryNumber' takes almost 40% of total execution time. This issue is partially caused by some unnecessary calls of this function (when calculating entropy of radical, we only need to know the symmetry number of the radical no need to calculate symmetry number of its saturated structure.) After modificaton, all the calculated thermo data is unchanged but implementation time of function 'calculateSymmetryNumber' is reduced from 40% to 12% of total execution time.