[aat.morx] Remove set_object() business

With OS X 10.13 Apple Chancery fails to ligate if we limit each morx
sub-chain to its declared length.  Perhaps their newer compiler does
object-sharing across sub-chains.  Anyway, since that's a valid, if
unspecified, way to compile tables, remove enforcement.

Probably do the same with kern/kerx.

src/hb-aat-layout-morx-table.hh

@@ -1026,8 +1026,6 @@ struct Chain
       if (reverse)
         c->buffer->reverse ();
 
-      c->sanitizer.set_object (*subtable);
-
       subtable->dispatch (c);
 
       if (reverse)
@@ -1041,7 +1039,6 @@ struct Chain
       subtable = &StructAfter<ChainSubtable<Types> > (*subtable);
       c->set_lookup_index (c->lookup_index + 1);
     }
-    c->sanitizer.reset_object ();
   }
 
   inline unsigned int get_size (void) const { return length; }
@@ -1061,15 +1058,10 @@ struct Chain
     unsigned int count = subtableCount;
     for (unsigned int i = 0; i < count; i++)
     {
-      c->reset_object ();
-      if (unlikely (!c->check_struct (subtable)))
-	return_trace (false);
-      c->set_object (*subtable);
       if (!subtable->sanitize (c))
 	return_trace (false);
       subtable = &StructAfter<ChainSubtable<Types> > (*subtable);
     }
-    c->reset_object ();
 
     return_trace (true);
   }