Merge into master from pull request #3453:

remove duplicate IFloodlightModules that provides debugCounter/debugEvent services (https://github.com/bigswitch/bigswitchcontroller/pull/3453)

src/main/resources/META-INF/services/net.floodlightcontroller.core.module.IFloodlightModule

@@ -17,9 +17,7 @@ net.floodlightcontroller.jython.JythonDebugInterface
 net.floodlightcontroller.counter.CounterStore
 net.floodlightcontroller.counter.NullCounterStore
 net.floodlightcontroller.debugcounter.DebugCounter
-net.floodlightcontroller.debugcounter.NullDebugCounter
 net.floodlightcontroller.debugevent.DebugEvent
-net.floodlightcontroller.debugevent.NullDebugEvent
 net.floodlightcontroller.threadpool.ThreadPool
 net.floodlightcontroller.ui.web.StaticWebRoutable
 net.floodlightcontroller.virtualnetwork.VirtualNetworkFilter