CameraServer: Change opencv sources to publish "cv:" type (#1412)

The LabVIEW dashboard has been fixed to understand this prefix.

cameraserver/src/main/java/edu/wpi/first/cameraserver/CameraServer.java

@@ -85,9 +85,7 @@ public final class CameraServer {
         }
       }
       case kCv:
-        // FIXME: Should be "cv:", but LabVIEW dashboard requires "usb:".
-        // https://github.com/wpilibsuite/allwpilib/issues/407
-        return "usb:";
+        return "cv:";
       default:
         return "unknown:";
     }