Remove unnecessary locking in DefaultNettyOptions

This value is initialized at constructor time and marked final, so it
can never change. There is no need to have access to this reference
synchronized.

Author: jasonk000

core/src/main/java/com/datastax/oss/driver/internal/core/context/DefaultNettyOptions.java

@@ -200,7 +200,7 @@ public Future<Void> onClose() {
   }
 
   @Override
-  public synchronized Timer getTimer() {
+  public Timer getTimer() {
     return timer;
   }
 }