Remove unncessary comment

Author: zsxwing

core/src/main/scala/org/apache/spark/rpc/RpcEnv.scala

@@ -38,8 +38,6 @@ private[spark] object RpcEnv {
     // Add more RpcEnv implementations here
     val rpcEnvNames = Map("akka" -> "org.apache.spark.rpc.akka.AkkaRpcEnvFactory",
       "netty" -> "org.apache.spark.rpc.netty.NettyRpcEnvFactory")
-    // Use "netty" by default so that Jenkins can run all tests using NettyRpcEnv.
-    // Will change it back to "akka" before merging the new implementation.
     val rpcEnvName = conf.get("spark.rpc", "netty")
     val rpcEnvFactoryClassName = rpcEnvNames.getOrElse(rpcEnvName.toLowerCase, rpcEnvName)
     Utils.classForName(rpcEnvFactoryClassName).newInstance().asInstanceOf[RpcEnvFactory]