[ML] Single Metric Viewer embeddable: ensure detector index is passed…

… to chart correctly (elastic#179761)

## Summary

This PR fixes bug where `selectedDetectorIndex` was not being passed to
the chart component correctly and always defaulted to the first
detector.

### Checklist

Delete any items that are not applicable to this PR.

- [ ] Any text added follows [EUI's writing
guidelines](https://elastic.github.io/eui/#/guidelines/writing), uses
sentence case text and includes [i18n
support](https://github.com/elastic/kibana/blob/main/packages/kbn-i18n/README.md)
- [ ]
[Documentation](https://www.elastic.co/guide/en/kibana/master/development-documentation.html)
was added for features that require explanation or tutorials
- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

(cherry picked from commit 80e2805)

x-pack/plugins/ml/public/embeddables/single_metric_viewer/embeddable_single_metric_viewer_container.tsx

@@ -69,7 +69,6 @@ export const EmbeddableSingleMetricViewerContainer: FC<
   const [chartWidth, setChartWidth] = useState<number>(0);
   const [zoom, setZoom] = useState<AppStateZoom | undefined>();
   const [selectedForecastId, setSelectedForecastId] = useState<string | undefined>();
-  const [detectorIndex, setDetectorIndex] = useState<number>(0);
   const [selectedJob, setSelectedJob] = useState<MlJob | undefined>();
   const [autoZoomDuration, setAutoZoomDuration] = useState<number | undefined>();
 
@@ -135,10 +134,6 @@ export const EmbeddableSingleMetricViewerContainer: FC<
        */
 
       switch (action) {
-        case APP_STATE_ACTION.SET_DETECTOR_INDEX:
-          setDetectorIndex(payload);
-          break;
-
         case APP_STATE_ACTION.SET_FORECAST_ID:
           setSelectedForecastId(payload);
           setZoom(undefined);
@@ -154,7 +149,7 @@ export const EmbeddableSingleMetricViewerContainer: FC<
       }
     },
 
-    [setZoom, setDetectorIndex, setSelectedForecastId]
+    [setZoom, setSelectedForecastId]
   );
 
   const containerPadding = 10;
@@ -185,7 +180,7 @@ export const EmbeddableSingleMetricViewerContainer: FC<
               lastRefresh={lastRefresh ?? 0}
               previousRefresh={previousRefresh}
               selectedJobId={selectedJobId}
-              selectedDetectorIndex={detectorIndex}
+              selectedDetectorIndex={data.selectedDetectorIndex}
               selectedEntities={data.selectedEntities}
               selectedForecastId={selectedForecastId}
               zoom={zoom}