The city marshal or chief of police and police officers of all cities located within, or a majority of the population of which reside within, any county adopting the provisions of this act, are hereby relieved of all power, authority and responsibility now or hereafter prescribed by law for the enforcement of laws of this state, ordinances of such city, the responsibility for the enforcement of which has been transferred to the county department and ordinances of such city the responsibility for the enforcement of which has by contract been placed in the county law enforcement department, from and after the date fixed for the transfer of such authority and responsibility to the law enforcement department under the provisions of this act.