With a strongly worded letter from the Amagansett Citizens Advisory Committee, the East Hampton Town Board cannot now assume that a plan to make a host of legal problems disappear at Cyril’s Fish House on Napeague — and allow the seasonally overcrowded business to grow — has much, if any, public support. Nonetheless, the board is set to go ahead with a public hearing tonight on an ill-advised scheme to downzone the parcel on which the bar and restaurant sits and an undeveloped lot next door from a residential to business classification.