Remove IOFSwitch.getChannel()

src/main/java/net/floodlightcontroller/core/IOFSwitch.java

...va/net/floodlightcontroller/core/internal/Controller.java

.../net/floodlightcontroller/core/internal/OFSwitchImpl.java

...a/net/floodlightcontroller/core/internal/RoleChanger.java

...ntroller/linkdiscovery/internal/LinkDiscoveryManager.java

...et/floodlightcontroller/core/internal/ControllerTest.java

...t/floodlightcontroller/core/internal/RoleChangerTest.java

.../floodlightcontroller/util/OFMessageDamperMockSwitch.java