Remove unused import

Author: Andrey Ershov

server/src/main/java/org/elasticsearch/cluster/coordination/JoinHelper.java

@@ -42,7 +42,6 @@
 import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.threadpool.ThreadPool.Names;
 import org.elasticsearch.transport.EmptyTransportResponseHandler;
-import org.elasticsearch.transport.RemoteTransportException;
 import org.elasticsearch.transport.TransportChannel;
 import org.elasticsearch.transport.TransportException;
 import org.elasticsearch.transport.TransportRequest;