A marked decline in the number of explosive devices coming into Iraq from neighboring Iran has helped reduce the frequency of deadly attacks against U.S. service members, a top U.S. general said Thursday. The military’s view reflects a growing belief that Iran has reduced its level of interference in Iraq and is no longer, as the U.S. alleges, providing weapons that are used to kill U.S. troops, potentially making it easier for the next administration to reach out to the government in Tehran.