revert elastic response parser

public/app/plugins/datasource/elasticsearch/elastic_response.js

@@ -76,12 +76,8 @@ function (_, queryDef) {
           newSeries = { datapoints: [], metric: metric.type, field: metric.field, props: props};
           for (i = 0; i < esAgg.buckets.length; i++) {
             bucket = esAgg.buckets[i];
-
-            value = bucket[metric.id];
-            if (value !== undefined) {
-              newSeries.datapoints.push([value.value, bucket.key]);
-            }
-
+            value = bucket[metric.id].value;
+            newSeries.datapoints.push([value, bucket.key]);
           }
           seriesList.push(newSeries);
           break;