Two taxi drivers were killed and four people injured in separate crashes in Hong Kong that struck within hours of each other.Police suspect that Tong Tak-shun, 65, passed out at the wheel from a possible heart attack while driving his taxi westbound along Fung Mat Road in the Western district shortly before midnight on Friday.When near to the Western Wholesale Food Market in Sai Wan, the vehicle careered out of control onto the wrong side of Water Street, before slamming into railings and…