BUG, TST: Fix tests of ma.count return type.

The masked array count method was fixed to use np.intp when doing sums.
The return type is always np.intp except for count(arr, axis=None) when
arr has no mask, in which case the return type is that of ndarray.size.

The test errors were noted in #4698.
Merge pull request #4699 from charris/fix-ma.count-return-type-check

BUG, TST: Fix tests of ma.count return type.