Remove unnecessary synchronization

The `videoSize` field is never written while holding the mutex, and is
only accessed from the same thread.

server/src/main/java/com/genymobile/scrcpy/video/NewDisplayCapture.java

@@ -241,7 +241,7 @@ public class NewDisplayCapture extends SurfaceCapture {
     }
 
     @Override
-    public synchronized Size getSize() {
+    public Size getSize() {
         return videoSize;
     }