Remove maximumHydrogenAtoms from documentation

Since it's not actually an implemented species constraint

Author: mliu49

documentation/source/users/rmg/input.rst

@@ -586,7 +586,6 @@ all of RMG's reaction families. ::
     generatedSpeciesConstraints(
         allowed=['input species','seed mechanisms','reaction libraries'],
         maximumCarbonAtoms=10,
-        maximumHydrogenAtoms=20,
         maximumOxygenAtoms=2,
         maximumNitrogenAtoms=2,
         maximumSiliconAtoms=2,