Remove useless imports and redundant type cast (#11639)

Motivation:

There are some redundant imports and unnecessary type cast

Modification:

Remove useless imports and unnecessary type cast

Result:

The code is cleaner than original

Signed-off-by: xingrufei <xingrufei@sogou-inc.com>

codec-mqtt/src/main/java/io/netty/handler/codec/mqtt/MqttMessageFactory.java

@@ -82,7 +82,7 @@ public final class MqttMessageFactory {
             case AUTH:
                 //Having MqttReasonCodeAndPropertiesVariableHeader
                 return new MqttMessage(mqttFixedHeader,
-                        (MqttReasonCodeAndPropertiesVariableHeader) variableHeader);
+                        variableHeader);
 
             default:
                 throw new IllegalArgumentException("unknown message type: " + mqttFixedHeader.messageType());

handler/src/main/java/io/netty/handler/ssl/ReferenceCountedOpenSslContext.java

@@ -56,7 +56,6 @@ import java.security.cert.CertificateNotYetValidException;
 import java.security.cert.CertificateRevokedException;
 import java.security.cert.X509Certificate;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.List;

transport-native-epoll/src/test/java/io/netty/channel/epoll/EpollSocketConnectTest.java

@@ -17,7 +17,6 @@ package io.netty.channel.epoll;
 
 import io.netty.bootstrap.Bootstrap;
 import io.netty.bootstrap.ServerBootstrap;
-import io.netty.channel.ChannelOption;
 import io.netty.testsuite.transport.TestsuitePermutation;
 import io.netty.testsuite.transport.socket.SocketConnectTest;