He would be remembered, colleagues said, as the father of the Sydney antique world. W.F. "Bill" Bradshaw, died yesterday at age 87. Just five months ago he sold his last piece, a fine English lacquer longcase clock. The former prime minister described him as ''simply the most knowledgeable antique dealer Australia has known.'' He lived his life with humor and ''on a diet of cheese, pickled onions and wedding cake.''