Revert r95841 due to failing media_unittests on linux_shared bot.

media/base/callback.h

Index: media/base/callback.h
===================================================================
--- media/base/callback.h	(revision 95843)
+++ media/base/callback.h	(working copy)
@@ -24,11 +24,10 @@
 #include "base/callback_old.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/task.h"
-#include "media/base/media_export.h"
 
 namespace media {
 
-class MEDIA_EXPORT AutoCallbackRunner {
+class AutoCallbackRunner {
  public:
   // Takes ownership of the callback.
   explicit AutoCallbackRunner(Callback0::Type* callback)