Remove cm->next_ref_frame_map, pbi->hold_ref_buf.

cm->next_ref_frame_map was intended to support frame parallel decoding.
Since frame parallel decoding was not implemented, we can remove
cm->next_ref_frame_map and the associated pbi->hold_ref_buf boolean.

swap_frame_buffers() is renamed update_frame_buffers() because the
function no longer swaps cm->ref_frame_map and cm->next_ref_frame_map;
now it updates cm->ref_frame_map. Also, release_frame_buffers() is
renamed release_current_frame() because the only frame buffer it
releases now is cm->current_frame.

TESTED=test_libaom --gtest_filter=*InvalidFileTest*

BUG=aomedia:2110,oss-fuzz:16437

Change-Id: I32dab3d01fb4574f2563f535c24804c6775933d2
diff --git a/test/test_data_util.cmake b/test/test_data_util.cmake
index 79aa88f..3206f59 100644
--- a/test/test_data_util.cmake
+++ b/test/test_data_util.cmake
@@ -547,6 +547,8 @@
               "invalid-oss-fuzz-11523.ivf.res.2"
               "invalid-oss-fuzz-15363.ivf"
               "invalid-oss-fuzz-15363.ivf.res"
+              "invalid-oss-fuzz-16437.ivf"
+              "invalid-oss-fuzz-16437.ivf.res"
               "invalid-oss-fuzz-9288.ivf"
               "invalid-oss-fuzz-9288.ivf.res"
               "invalid-oss-fuzz-9463.ivf"