Simplify icon example and show popup at clicked position

By using the event's coordinate instead of the feature's, we make sure
that the popup is shown where the user clicked when on a wrapped world.

examples/icon.js

@@ -71,9 +71,7 @@ map.on('click', function(evt) {
         return feature;
       });
   if (feature) {
-    var geometry = feature.getGeometry();
-    var coord = geometry.getCoordinates();
-    popup.setPosition(coord);
+    popup.setPosition(evt.coordinate);
     $(element).popover({
       'placement': 'top',
       'html': true,