A new book offers striking stories about 71 Delaware landmarks that “now live solely in memory,” from the Greenbaum cannery (a Seaford operation that was sometimes described as the world’s biggest and was known for canning tomatoes, peas, peaches and pears) to the Cape Henlopen Light (a beacon that operated from 1767 to about 12:45 p.m. April 13, 1926, when …