Remove assertions which compare the sum of weights between passes.

Remove assertions which compare the sum of weights between passes.

These asserted that the sum of case-weights of a dataset calculated
in one pass, was the same as that calculated in a second pass.
Algebraically this is correct.  However, for optimisation purposes,
it is sometimes desireable that the second pass occurs after the
data has been reordered.   If that happens, the sum of weights can
be slightly different due to floating point rounding errors.  This
happens particularly when the caseweights are fractional.