Redundant methods in SymbolicTwoPointBVP

[davidrpugh]

These methods...

   def _validate_boundary(self, conditions):
        """Validate a dictionary of lower and upper boundary conditions."""
        super(SymbolicTwoPointBVP, self)._validate_boundary(conditions)
        bcs = {'lower': self._validate_boundary_exprs(conditions['lower']),
               'upper': self._validate_boundary_exprs(conditions['upper'])}
        return bcs

    def _validate_boundary_exprs(self, expressions):
        """Check that lower/upper boundary_conditions are expressions."""
        if expressions is None:
            return None
        else:
            return [self._validate_expression(expr) for expr in expressions]

...are redundant and should be removed.