Remove ignored return code from modules.

ModuleProcessImpl doesn't act on return codes and having them around is
confusing (it's unclear what an error return code here would do even).

BUG=
R=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1703833002 .

Cr-Commit-Position: refs/heads/master@{#11747}

webrtc/modules/video_render/video_render_impl.h

@@ -35,7 +35,7 @@ public:
     virtual ~ModuleVideoRenderImpl();
 
     virtual int64_t TimeUntilNextProcess();
-    virtual int32_t Process();
+    virtual void Process();
 
     /*
      *   Returns the render window