comment out "average speed" card

"Average speed" needs to be handled differently because it is not mathematically correct to average it across days without considering differences in distance and duration between those days.
(described in e-mission/e-mission-docs#961)

We can comment this out; maybe revisit later

www/js/metrics/MetricsTab.tsx

@@ -97,11 +97,11 @@ const MetricsTab = () => {
           aggMetricsDays={aggMetrics?.duration}
           axisUnits={t('metrics.hours')}
           unitFormatFn={secondsToHours} />
-        <MetricsCard cardTitle={t('main-metrics.mean-speed')}
+        {/* <MetricsCard cardTitle={t('main-metrics.mean-speed')}
           userMetricsDays={userMetrics?.mean_speed}
           aggMetricsDays={aggMetrics?.mean_speed}
           axisUnits={speedSuffix}
-          unitFormatFn={getFormattedSpeed} />
+          unitFormatFn={getFormattedSpeed} /> */}
       </Carousel>
     </ScrollView>
   </>);