The city council in a city and township described in Section 15-45 may by ordinance provide (i) that the offices of city and township clerk are united in the same person, (ii) that the offices of city treasurer and township collector are united in the same person, and (iii) that the office and election of highway commissioners shall be discontinued. In any combination of offices under this Section, the combined office shall be filled in the manner provided by law for filling the office of city clerk or city treasurer, as the case may be. The township supervisor shall be, ex officio, supervisor of general assistance.