[subset] Write out a format 4, plat 0 encoding record to match fontTools.

test/api/test-subset-cmap.c

diff --git a/test/api/test-subset-cmap.c b/test/api/test-subset-cmap.c
index 5254874..8c51938 100644
--- a/test/api/test-subset-cmap.c
+++ b/test/api/test-subset-cmap.c
@@ -33,7 +33,7 @@
 test_subset_cmap (void)
 {
   hb_face_t *face_abc = hb_subset_test_open_font ("fonts/Roboto-Regular.abc.ttf");
-  hb_face_t *face_ac = hb_subset_test_open_font ("fonts/Roboto-Regular.ac.cmap-format12-only.ttf");
+  hb_face_t *face_ac = hb_subset_test_open_font ("fonts/Roboto-Regular.ac.ttf");
 
   hb_set_t *codepoints = hb_set_create ();
   hb_face_t *face_abc_subset;