Disable the TestSuperframeIndexIsOptional test with ANS.

Change-Id: Id55a741e2015c4e01d156d3fe5319498b016b9cf

test/superframe_test.cc

@@ -108,7 +108,11 @@ VP9_INSTANTIATE_TEST_CASE(SuperframeTest, ::testing::Combine(
     ::testing::Values(::libvpx_test::kTwoPassGood),
     ::testing::Values(0)));
 
+// The superframe index is currently mandatory with ANS due to the decoder
+// starting at the end of the buffer.
+#if !CONFIG_ANS
 VP10_INSTANTIATE_TEST_CASE(SuperframeTest, ::testing::Combine(
     ::testing::Values(::libvpx_test::kTwoPassGood),
     ::testing::Values(1)));
+#endif
 }  // namespace