[subset/hdmx] Speed up

src/hb-ot-hdmx-table.hh

@@ -125,7 +125,7 @@ struct hdmx
 	    | hb_map (c->plan->reverse_glyph_map)
 	    | hb_map ([this, c, device_record] (hb_codepoint_t _)
 		      {
-			if (c->plan->is_empty_glyph (_))
+			if (_ == HB_MAP_VALUE_INVALID)
 			  return Null (HBUINT8);
 			return device_record->widthsZ.as_array (get_num_glyphs ()) [_];
 		      })

src/hb-subset-plan.hh

@@ -188,15 +188,6 @@ struct hb_subset_plan_t
     return _num_output_glyphs;
   }
 
-  /*
-   * Given an output gid , returns true if that glyph id is an empty
-   * glyph (ie. it's a gid that we are dropping all data for).
-   */
-  inline bool is_empty_glyph (hb_codepoint_t gid) const
-  {
-    return !_glyphset.has (gid);
-  }
-
   inline bool new_gid_for_codepoint (hb_codepoint_t codepoint,
 				     hb_codepoint_t *new_gid) const
   {