Remove unnecessary import

Author: Stephane Maldini

spring-webflux/src/main/java/org/springframework/web/reactive/socket/adapter/ReactorNettyWebSocketSession.java

@@ -21,7 +21,6 @@
 import reactor.core.publisher.Mono;
 import reactor.netty.NettyInbound;
 import reactor.netty.NettyOutbound;
-import reactor.netty.NettyPipeline;
 import reactor.netty.http.websocket.WebsocketInbound;
 import reactor.netty.http.websocket.WebsocketOutbound;