[subset] Convert offset serialization in gsubgpos and gdef to serialize_serialize().

src/hb-ot-layout-gdef-table.hh

diff --git a/src/hb-ot-layout-gdef-table.hh b/src/hb-ot-layout-gdef-table.hh
index edb35da..31a4a3e 100644
--- a/src/hb-ot-layout-gdef-table.hh
+++ b/src/hb-ot-layout-gdef-table.hh
@@ -98,8 +98,7 @@
     | hb_map (glyph_map)
     | hb_sink (new_coverage)
     ;
-    out->coverage.serialize (c->serializer, out)
-		 .serialize (c->serializer, new_coverage.iter ());
+    out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
     return_trace (bool (new_coverage));
   }
 
@@ -386,8 +385,7 @@
     | hb_map (glyph_map)
     | hb_sink (new_coverage)
     ;
-    out->coverage.serialize (c->serializer, out)
-		 .serialize (c->serializer, new_coverage.iter ());
+    out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
     return_trace (bool (new_coverage));
   }
 

src/hb-ot-layout-gsubgpos.hh

diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index fb86311..926b144 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -1898,8 +1898,7 @@
     | hb_sink (new_coverage)
     ;
 
-    out->coverage.serialize (c->serializer, out)
-		 .serialize (c->serializer, new_coverage.iter ());
+    out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
     return_trace (bool (new_coverage));
   }
 
@@ -2866,8 +2865,7 @@
     | hb_sink (new_coverage)
     ;
 
-    out->coverage.serialize (c->serializer, out)
-		 .serialize (c->serializer, new_coverage.iter ());
+    out->coverage.serialize_serialize (c->serializer, new_coverage.iter ());
     return_trace (bool (new_coverage));
   }