Clean up warnings and delete dead code

spring-websocket/src/test/java/org/springframework/web/socket/sockjs/transport/handler/HttpReceivingTransportHandlerTests.java

@@ -18,7 +18,6 @@ package org.springframework.web.socket.sockjs.transport.handler;
 
 import org.junit.Test;
 
-import org.springframework.http.MediaType;
 import org.springframework.web.socket.AbstractHttpRequestTests;
 import org.springframework.web.socket.TextMessage;
 import org.springframework.web.socket.WebSocketHandler;