Clean up spring-websocket imports

spring-websocket is full of unused imports. This commit removes all
unused imports from spring-websocket.

spring-websocket/src/main/java/org/springframework/web/socket/adapter/standard/StandardWebSocketSession.java

@@ -30,7 +30,6 @@ import javax.websocket.Extension;
 import javax.websocket.Session;
 
 import org.springframework.http.HttpHeaders;
-import org.springframework.util.StringUtils;
 import org.springframework.web.socket.BinaryMessage;
 import org.springframework.web.socket.CloseStatus;
 import org.springframework.web.socket.PingMessage;

spring-websocket/src/main/java/org/springframework/web/socket/config/annotation/WebSocketMessageBrokerConfigurationSupport.java

@@ -18,7 +18,6 @@ package org.springframework.web.socket.config.annotation;
 
 import org.springframework.context.annotation.Bean;
 import org.springframework.messaging.simp.config.AbstractMessageBrokerConfiguration;
-import org.springframework.messaging.simp.config.MessageBrokerRegistry;
 import org.springframework.messaging.simp.user.UserSessionRegistry;
 import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
 import org.springframework.web.servlet.HandlerMapping;

spring-websocket/src/main/java/org/springframework/web/socket/messaging/SessionDisconnectEvent.java

@@ -18,7 +18,6 @@ package org.springframework.web.socket.messaging;
 
 
 import org.springframework.context.ApplicationEvent;
-import org.springframework.messaging.Message;
 import org.springframework.util.Assert;
 import org.springframework.web.socket.CloseStatus;
 

spring-websocket/src/main/java/org/springframework/web/socket/messaging/SubProtocolWebSocketHandler.java

@@ -16,7 +16,6 @@
 
 package org.springframework.web.socket.messaging;
 
-import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashSet;

spring-websocket/src/main/java/org/springframework/web/socket/server/HandshakeInterceptor.java

@@ -21,7 +21,6 @@ import java.util.Map;
 import org.springframework.http.server.ServerHttpRequest;
 import org.springframework.http.server.ServerHttpResponse;
 import org.springframework.web.socket.WebSocketHandler;
-import org.springframework.web.socket.WebSocketSession;
 
 /**
  * Interceptor for WebSocket handshake requests. Can be used to inspect the

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/support/AbstractSockJsService.java

@@ -44,7 +44,6 @@ import org.springframework.util.StringUtils;
 import org.springframework.web.socket.WebSocketHandler;
 import org.springframework.web.socket.sockjs.SockJsException;
 import org.springframework.web.socket.sockjs.SockJsService;
-import org.springframework.web.util.UriComponentsBuilder;
 
 /**
  * An abstract base class for {@link SockJsService} implementations that provides SockJS

spring-websocket/src/main/java/org/springframework/web/socket/sockjs/transport/session/PollingSockJsSession.java

@@ -18,7 +18,6 @@ package org.springframework.web.socket.sockjs.transport.session;
 
 import java.util.Map;
 import java.util.Queue;
-import java.util.concurrent.BlockingQueue;
 
 import org.springframework.web.socket.WebSocketHandler;
 import org.springframework.web.socket.sockjs.SockJsTransportFailureException;

spring-websocket/src/test/java/org/springframework/web/socket/client/standard/StandardWebSocketClientTests.java

@@ -30,9 +30,7 @@ import org.junit.Before;
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
 
-import org.springframework.core.task.AsyncListenableTaskExecutor;
 import org.springframework.core.task.SimpleAsyncTaskExecutor;
-import org.springframework.core.task.TaskExecutor;
 import org.springframework.web.socket.WebSocketHandler;
 import org.springframework.web.socket.WebSocketSession;
 import org.springframework.web.socket.handler.AbstractWebSocketHandler;

spring-websocket/src/test/java/org/springframework/web/socket/config/MessageBrokerBeanDefinitionParserTests.java

@@ -64,7 +64,6 @@ import org.springframework.web.socket.sockjs.transport.handler.DefaultSockJsServ
 import org.springframework.web.socket.sockjs.transport.handler.WebSocketTransportHandler;
 
 import static org.junit.Assert.*;
-import static org.junit.Assert.assertEquals;
 
 /**
  * Test fixture for MessageBrokerBeanDefinitionParser.

spring-websocket/src/test/java/org/springframework/web/socket/handler/ConcurrentWebSocketSessionDecoratorTests.java

@@ -28,7 +28,6 @@ import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 
 import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 

spring-websocket/src/test/java/org/springframework/web/socket/messaging/StompSubProtocolHandlerTests.java

@@ -49,7 +49,6 @@ import org.springframework.web.socket.handler.TestWebSocketSession;
 import org.springframework.web.socket.sockjs.transport.SockJsSession;
 
 import static org.junit.Assert.*;
-import static org.junit.Assert.assertEquals;
 import static org.mockito.Mockito.*;
 
 /**