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}
diff --git a/webrtc/modules/media_file/media_file_impl.h b/webrtc/modules/media_file/media_file_impl.h
index c23f514..677098e 100644
--- a/webrtc/modules/media_file/media_file_impl.h
+++ b/webrtc/modules/media_file/media_file_impl.h
@@ -26,7 +26,7 @@
     MediaFileImpl(const int32_t id);
     ~MediaFileImpl();
 
-    int32_t Process() override;
+    void Process() override;
     int64_t TimeUntilNextProcess() override;
 
     // MediaFile functions