Remove DISALLOW_ macro from libcef_dll/ (see issue #3234)

Also perform related C++ cleanup:
- Use =default instead of {} for default implementations of
  constructors/destructors.
- Replace typedef with using.

include/wrapper/cef_closure_task.h

@@ -38,7 +38,6 @@
 #pragma once
 
 #include "include/base/cef_callback_forward.h"
-#include "include/base/cef_macros.h"
 #include "include/cef_task.h"
 
 ///