Remove ChangeUniqueID.

This fixes a two year old TODO of deleting dead code :)
In cases where the _id or id_ member variable is being used for tracing,
I changed the member to at least be const.

It doesn't look like id's are that useful anymore so maybe the next step is to get rid of them.

BUG=
R=henrika@webrtc.org, perkj@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/37849004

Cr-Commit-Position: refs/heads/master@{#8201}
git-svn-id: http://webrtc.googlecode.com/svn/trunk@8201 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_render/include/video_render.h

@@ -52,13 +52,6 @@ public:
      */
     static void DestroyVideoRender(VideoRender* module);
 
-    /*
-     *   Change the unique identifier of this object
-     *
-     *   id      - new unique identifier of this video render module object
-     */
-    virtual int32_t ChangeUniqueId(const int32_t id) OVERRIDE = 0;
-
     virtual int64_t TimeUntilNextProcess() OVERRIDE = 0;
     virtual int32_t Process() OVERRIDE = 0;