CHARLESTON, S.C. — It turns out a historic amount of rain was only the second — or maybe even the third — biggest obstacle the golfing fanatics of the Boston Celtics encountered during the team’s stay in South Carolina’s Lowcountry this week. The National Weather Service recorded 3.64 inches of rainfall in Charleston on Sunday, obliterating the 133-year-old record of 2.51 inches set in 1893. The rain saturated local courses and deterred the tea…