LONG BEACH, Calif. — Dwindling domestic demand for C-17 cargo planes will force Boeing Co. to slash 1,100 jobs at its U.S. plants, most of them in Long Beach where the aerospace giant has cut 13,000 jobs since the 1990s, the company said Thursday.The 900 jobs in Long Beach and 200 jobs at plants in Mesa, Ariz., Macon, Ga., and St.