GONE FLAT: After 46 years, Ontario's A&W Drive-In, the only location in Southern California with carhop service, is closing April 30. Owners Larry and Sherrill Roan are retiring after devoting more than half their lives to the restaurant at 1267 W. Holt Blvd. With sales down, and corporate interest waning, the root beer specialists can no longer stay afloat. Photo Gallery: A&W Drive-In closing So much for "Happy Days.'' "We sold the property,'' Larry told me from behind the counter when I stopped by to ask about the rumored closing. "It won't be a restaurant,'' he added. "It'll probably be...