GetMetricStatistics API returns many zero SampleCounts for sparse metrics

For sparse metrics (i.e. where there exist only relatively few actual datapoints), the responses to calls on the GetMetricStatistics API seeking the SampleCount statistic are polluted with many trivial datapoints for the periods in which there were no metrics reported.

This is unnecessary and bloats the response with meaningless data that could be inferred.

Note that this only occurs for the SampleCount statistic, i.e. a zero Sum is not reported for periods in which no actual datapoints exist.

The null sample counts should be excised from the GetMetricStatistics response.