Replace the remaining scoped_ptr with unique_ptr in webrtc/modules/

BUG=webrtc:5520

Review URL: https://codereview.webrtc.org/1921233002

Cr-Commit-Position: refs/heads/master@{#12511}

webrtc/modules/video_coding/packet_buffer.h

@@ -14,11 +14,11 @@
 #include <array>
 #include <vector>
 #include <map>
+#include <memory>
 #include <set>
 #include <queue>
 
 #include "webrtc/base/criticalsection.h"
-#include "webrtc/base/scoped_ptr.h"
 #include "webrtc/base/thread_annotations.h"
 #include "webrtc/modules/video_coding/packet.h"
 #include "webrtc/modules/video_coding/sequence_number_util.h"