Whenever there exists within the corporate limits of the City of Pleasanton adjoining the outer boundaries thereof any territory not suitable or necessary for orderly planning and development of the City, the City Council may, upon a petition signed by a majority of the qualified voters residing in such territory, if the same be inhabited, or without any such petition if the same be uninhabited, by ordinance duly passed, de-annex such territory as a part of said city; and after the entry of such ordinance said territory and the inhabitants thereof shall cease to be a part of the city.