Remove I440 image support from libaom API and tools.

ABI is unaffected.

BUG=aomedia:1672

Change-Id: I12f88f396bd8c3c814a5a554a4702cc35036e858
diff --git a/av1/av1_iface_common.h b/av1/av1_iface_common.h
index 7e76326..59db776 100644
--- a/av1/av1_iface_common.h
+++ b/av1/av1_iface_common.h
@@ -30,13 +30,8 @@
       bps = 16;
     }
   } else {
-    if (!yv12->subsampling_x) {
-      img->fmt = AOM_IMG_FMT_I440;
-      bps = 16;
-    } else {
-      img->fmt = AOM_IMG_FMT_I420;
-      bps = 12;
-    }
+    img->fmt = AOM_IMG_FMT_I420;
+    bps = 12;
   }
   img->cp = yv12->color_primaries;
   img->tc = yv12->transfer_characteristics;