Remove todo that is no longer applicable (#208)

There's no need to stop sending MetricKind, as we actually do that in
the
[collector](https://cs.github.com/GoogleCloudPlatform/opentelemetry-operations-go/blob/e955c204f4f2bfdc92ff0ad52786232b975efcc2/exporter/metric/metric.go?q=createtimeseries#L479).
I don't think it's worth keeping a todo around.

Author: aabmass

opentelemetry-exporter-gcp-monitoring/src/opentelemetry/exporter/cloud_monitoring/__init__.py

@@ -326,8 +326,6 @@ def export(
                         )
                         series = TimeSeries(
                             resource=monitored_resource,
-                            # TODO: remove
-                            # https://github.com/GoogleCloudPlatform/opentelemetry-operations-python/issues/84
                             metric_kind=descriptor.metric_kind,
                             points=[point],
                             metric=GMetric(