Whenever any city shall own any building or equipment which was constructed or purchased by the issuance of municipal revenue bonds or which building or equipment has been previously used by such city in its proprietary function and the governing body of such city shall find and declare by ordinance that such building or equipment is no longer used or needed by such city in its proprietary function of furnishing water, gas, light, heat or for other public utility purposes, then such city is authorized and empowered to alter, improve, repair, equip and use for any governmental function or purpose any such building or equipment or any part thereof as the governing body of such city may determine and declare by ordinance.