Remove RegisterExternal{De,En}coder error codes.

webrtc/modules/video_coding/video_coding_robustness_unittest.cc

Index: webrtc/modules/video_coding/video_coding_robustness_unittest.cc
diff --git a/webrtc/modules/video_coding/video_coding_robustness_unittest.cc b/webrtc/modules/video_coding/video_coding_robustness_unittest.cc
index 9c4976c30d823d429306c49b2e65d02a8dded151..d5a179dccbb270f8ea7448b995d278547b3a8310 100644
--- a/webrtc/modules/video_coding/video_coding_robustness_unittest.cc
+++ b/webrtc/modules/video_coding/video_coding_robustness_unittest.cc
@@ -44,9 +44,7 @@ class VCMRobustnessTest : public ::testing::Test {
     ASSERT_EQ(0, vcm_->RegisterPacketRequestCallback(&request_callback_));
     ASSERT_EQ(VCM_OK, vcm_->Codec(kVideoCodecVP8, &video_codec_));
     ASSERT_EQ(VCM_OK, vcm_->RegisterReceiveCodec(&video_codec_, 1));
-    ASSERT_EQ(VCM_OK, vcm_->RegisterExternalDecoder(&decoder_,
-                                                    video_codec_.plType,
-                                                    true));
+    vcm_->RegisterExternalDecoder(&decoder_, video_codec_.plType, true);
   }
 
   virtual void TearDown() {