removed legacy time conversion for graph

* caused the graph to have incorrect timestamps, in turn causing
  the timebox to display incorrect time during mouse hover

Author: rossengeorgiev

js/tracker.js

@@ -875,9 +875,7 @@ function graphAddLastPosition(idx) {
     vehicles[idx].graph_data_updated = true;
     var data = vehicles[idx].graph_data;
     var new_data = vehicles[idx].curr_position;
-    var date = new Date(convert_time(new_data.gps_time));
-    var tz_offset_milis = date.getTimezoneOffset() * 60000;
-    var ts = date.getTime() - tz_offset_milis;
+    var ts = convert_time(new_data.gps_time);
 
     if(vehicles[idx].graph_data.length) {
         var ts_last_idx = data[0].data.length - 1;