Add XLALDestroySSBtimes(), the single detector equivalent of XLALDestroyMultiSSBtimes

- refs #1404
timeDiff is floating point, use fabs()
use fabs() for floating point
n is an integer, use abs()
use fabs() for floating point
use fabs() for floating point
use fabs() for floating point
test of array to null pointer is always false