Say goodbye to the late-night fries and gravy. One of the last classic Brooklyn diners is biting the dust — and soon they’ll all die off due to the state’s minimum-wage increase and other factors, restaurateurs and economic experts predicted Friday. The owner of the four-decade-old, 24-hour greasy spoon, Del Rio Diner in Gravesend, said his place is closing down because he can’t afford to pay cooks $15 an hour, along with rising rents and expensive Health Department inspection fees. …