As the City Planning Commission prepares to consider a plan to create a historic district that would, in effect, make every house in Riverdale’s Fieldston section a landmark, the neighborhood’s most prominent religious leader has declared that he opposes the proposal.The senior rabbi of the Hebrew Institute of Riverdale, Rabbi Avi Weiss, declared that the net result of the proposed landmarking will be harmful to the area’s Orthodox Jewish community. If the Planning Commission approves the project on Wednesday, it will then go before the City Council….