Fix a build warning - a source file was specified multiple times.

Change-Id: I2e7d4887648fad0cfcdb3f59fcc9fda7673dde72
diff --git a/Android.mk b/Android.mk
index a475016..bf8e58d 100644
--- a/Android.mk
+++ b/Android.mk
@@ -49,7 +49,6 @@
     vp8/decoder/generic/dsystemdependent.c \
     vp8/decoder/onyxd_if.c \
     vp8/decoder/threading.c \
-    vp8/vp8_dx_iface.c \
     vpx_config.c \
     vp8/decoder/arm/neon/idct_blk_neon.c