JERUSALEM (AP) — When the onetime director of a Gaza Strip hospital was killed by an Israeli airstrike last week, he joined a growing list of prominent Palestinian doctors who have died during 21 months of war that has devastated the territory’s health system. The death of Dr. Marwan al-Sultan, a 49-year-old cardiologist, was described by colleagues as a major blow personally and professionally, leaving another void in Gaza’s medical establishment that will not be easily replaced. “He was one of two cardiologists, so by losing Dr. Marwan, thousands of people will lose and suffer,” said Mohammed Abu Selmia, a close friend of his for 15 years, and the director of Shifa Hospital, Gaza’s largest medical facility.