Replace scoped_ptr with unique_ptr in webrtc/modules/

Except in places where this would break out-of-tree code,
such as Chromium.

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1785173002

Cr-Commit-Position: refs/heads/master@{#12037}

webrtc/modules/video_coding/nack_module_unittest.cc

@@ -9,6 +9,8 @@
  */
 
 #include <cstring>
+#include <memory>
+
 #include "testing/gtest/include/gtest/gtest.h"
 #include "webrtc/modules/video_coding/include/video_coding_defines.h"
 #include "webrtc/modules/video_coding/nack_module.h"