Remove duplicate code in test/webm_video_source.h

Remove duplicate WebM parsing code in test/webm_video_source.h and linking it
against webmdec.c which does the exact same thing.

Change-Id: Ib7152eecde890fca58be42028cab18c9cb54221c
diff --git a/test/test.mk b/test/test.mk
index 92664e2..f1a8ed9 100644
--- a/test/test.mk
+++ b/test/test.mk
@@ -49,6 +49,9 @@
 NESTEGG_SRCS                           += ../third_party/nestegg/include/nestegg/nestegg.h
 NESTEGG_SRCS                           += ../third_party/nestegg/src/nestegg.c
 LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += $(NESTEGG_SRCS)
+LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += ../tools_common.h
+LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += ../webmdec.c
+LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += ../webmdec.h
 LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += webm_video_source.h
 
 LIBVPX_TEST_SRCS-$(CONFIG_DECODERS)    += test_vector_test.cc