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/linux/video_render_linux_impl.cc

@@ -61,14 +61,6 @@ int32_t VideoRenderLinuxImpl::Init()
 
 }
 
-int32_t VideoRenderLinuxImpl::ChangeUniqueId(const int32_t id)
-{
-    CriticalSectionScoped cs(&_renderLinuxCritsect);
-
-    _id = id;
-    return 0;
-}
-
 int32_t VideoRenderLinuxImpl::ChangeWindow(void* window)
 {
     WEBRTC_TRACE(kTraceInfo, kTraceVideoRenderer, _id, "%s",

webrtc/modules/video_render/linux/video_render_linux_impl.h

@@ -34,8 +34,6 @@ public:
 
     virtual int32_t Init();
 
-    virtual int32_t ChangeUniqueId(const int32_t id);
-
     virtual int32_t ChangeWindow(void* window);
 
     /**************************************************************************