Another San Mateo County landmark is going to bite the dust within the next five years or so. Speaking this past week in Burlingame, John Martin, director of San Francisco International Airport, said the 196-foot-tall SFO air traffic control tower has to be torn down, most probably within that time frame, because it is seismically unstable and could be unusable in the event of a major earthquake. A new tower would be built either in the same location _ where the vacant Central Terminal resides _ or somewhere else on the SFO property east of Highway 101. That terminal is scheduled to be either renovated or razed and rebuilt within five years, Martin explained.