By Humeyra PamukWASHINGTON, March 6 (Reuters) - The United States is pressing Sri Lanka's government not to repatriate the survivors from the Iranian warship it sank this week, as well as the crew of a second Iranian ship that is in Sri Lankan custody, according to an internal State Department cable seen by Reuters on Friday. A U.S. submarine sank the IRIS Dena warship in the Indian Ocean about 19 nautical miles off Sri Lanka's southern port city of Galle on Wednesday, killing dozens of sailors...