Don't remove milestone listener on arrival / adjust arrival verbiage

Author: danesfeder

navigation/libandroid-navigation/src/main/java/com/mapbox/services/android/navigation/v5/navigation/DefaultMilestones.java

@@ -194,6 +194,6 @@ public String buildInstruction(RouteProgress routeProgress) {
   private String getInstructionString(RouteProgress routeProgress) {
     return routeProgress.currentLegProgress().upComingStep() != null
       ? routeProgress.currentLegProgress().upComingStep().getManeuver().getInstruction() :
-      "Arrived at your destination";
+      "You have arrived";
   }
 }

navigation/libandroid-navigation/src/main/java/com/mapbox/services/android/navigation/v5/navigation/MapboxNavigation.java

@@ -603,7 +603,6 @@ public void onProgressChange(Location location, RouteProgress routeProgress) {
     NavigationMetricsWrapper.arriveEvent(sessionState, routeProgress, location);
     // Remove all listeners except the onProgressChange by passing in null.
     navigationEventDispatcher.removeOffRouteListener(null);
-    navigationEventDispatcher.removeMilestoneEventListener(null);
     // Remove this listener so that the arrival event only occurs once.
     navigationEventDispatcher.removeInternalProgressChangeListener();
   }