Fix server checkstyle errors

Fix errors reported by:

    gradle -p server check

server/src/main/java/com/genymobile/scrcpy/EventController.java

@@ -1,7 +1,6 @@
 package com.genymobile.scrcpy;
 
 import com.genymobile.scrcpy.wrappers.InputManager;
-import com.genymobile.scrcpy.wrappers.ServiceManager;
 
 import android.graphics.Point;
 import android.os.SystemClock;

server/src/main/java/com/genymobile/scrcpy/IO.java

@@ -8,7 +8,7 @@ import java.io.FileDescriptor;
 import java.io.IOException;
 import java.nio.ByteBuffer;
 
-public class IO {
+public final class IO {
     private IO() {
         // not instantiable
     }

server/src/main/java/com/genymobile/scrcpy/ScreenEncoder.java

@@ -3,7 +3,6 @@ package com.genymobile.scrcpy;
 import com.genymobile.scrcpy.wrappers.SurfaceControl;
 
 import android.graphics.Rect;
-import android.media.MediaMuxer;
 import android.media.MediaCodec;
 import android.media.MediaCodecInfo;
 import android.media.MediaFormat;

server/src/main/java/com/genymobile/scrcpy/Server.java

@@ -4,7 +4,6 @@ import android.graphics.Rect;
 
 import java.io.File;
 import java.io.IOException;
-import java.util.Arrays;
 
 public final class Server {
 
@@ -49,8 +48,9 @@ public final class Server {
 
     @SuppressWarnings("checkstyle:MagicNumber")
     private static Options createOptions(String... args) {
-        if (args.length != 5)
+        if (args.length != 5) {
             throw new IllegalArgumentException("Expecting 5 parameters");
+        }
 
         Options options = new Options();
 
@@ -73,6 +73,7 @@ public final class Server {
         return options;
     }
 
+    @SuppressWarnings("checkstyle:MagicNumber")
     private static Rect parseCrop(String crop) {
         if ("-".equals(crop)) {
             return null;

server/src/main/java/com/genymobile/scrcpy/wrappers/StatusBarManager.java

@@ -1,8 +1,6 @@
 package com.genymobile.scrcpy.wrappers;
 
-import android.annotation.SuppressLint;
 import android.os.IInterface;
-import android.view.InputEvent;
 
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;