[tz] McMurdo/South Pole

Since McMurdo was not founded until 16 Feb 1956 (wikipedia), I think that it is simply incorrect data to assign any time-zone transitions until that date. There simply were no DST transitions in McMurdo in the 1930s as it did not exist. https://github.com/jodastephen/tzdiff/commit/57aac13605f184a46f74d22f7dddc90... This is a a case where an ID that has existed for a long time with reasonably good data that has now been degraded through a Zone to Link conversion. Stephen (I hadn't realised the extent of the data pollution of McMurdo until I did my recent data analysis)