gdb: remove TYPE_FIELD macro

Replace all uses of it by type::field.

Note that since type::field returns a reference to the field, some spots
are used to assign the whole field structure.  See ctfread.c, function
attach_fields_to_type, for example.  This is the same as was happening
with the macro, so I don't think it's a problem, but if anybody sees a
really nicer way to do this, now could be a good time to implement it.

gdb/ChangeLog:

	* gdbtypes.h (TYPE_FIELD): Remove.  Replace all uses with
	type::field.

gdb/symtab.c

@@ -1973,7 +1973,7 @@ check_field (struct type *type, const char *name,
       if (t_field_name && (strcmp_iw (t_field_name, name) == 0))
 	{
 	  is_a_field_of_this->type = type;
-	  is_a_field_of_this->field = &TYPE_FIELD (type, i);
+	  is_a_field_of_this->field = &type->field (i);
 	  return 1;
 	}
     }