Remove useless symbols from the grammar.
        Useless symbols are unreachable or nongenerating one.
        :param grammar: Grammar where to symbols remove
        :param inplace: True if transformation should be performed in place, false otherwise.
        False by default.
        :return: Grammar without useless symbols.

def remove_useless_symbols(grammar, inplace=False):
        # type: (Grammar, bool) -> Grammar
        """
        Remove useless symbols from the grammar.
        Useless symbols are unreachable or nongenerating one.
        :param grammar: Grammar where to symbols remove
        :param inplace: True if transformation should be performed in place, false otherwise.
        False by default.
        :return: Grammar without useless symbols.
        """
        grammar = ContextFree.remove_nongenerating_nonterminals(grammar, inplace)
        grammar = ContextFree.remove_unreachable_symbols(grammar, True)
        return grammar