Remove unused imports.

apm-sniffer/apm-agent-core/src/main/java/org/skywalking/apm/agent/core/jvm/JVMService.java

 package org.skywalking.apm.agent.core.jvm;
 
 import io.grpc.ManagedChannel;
-import java.text.SimpleDateFormat;
-import java.util.Date;
 import java.util.LinkedList;
 import java.util.concurrent.Executors;
 import java.util.concurrent.LinkedBlockingQueue;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
-import java.util.concurrent.locks.ReentrantLock;
 import org.skywalking.apm.agent.core.boot.BootService;
 import org.skywalking.apm.agent.core.boot.ServiceManager;
 import org.skywalking.apm.agent.core.conf.Config;