Deprecate metrics methods

Metrics are controlled via bstats config for some time now. The config option in settings.yml has already been deprecated in the past.

Bukkit/src/main/java/com/github/intellectualsites/plotsquared/bukkit/BukkitMain.java

@@ -682,6 +682,8 @@ public final class BukkitMain extends JavaPlugin implements Listener, IPlotMain
         return new BukkitSetupUtils();
     }
 
+    @Deprecated
+    // Metrics are controlled via bstats config
     @Override public void startMetrics() {
         if (this.metricsStarted) {
             return;