Fix misleading comment in pg_get_statisticsobjdef_string()

The comment claimed that a TABLESPACE reference was added to the
resulting string, but that's not true.  Looks like the comment was
copied from pg_get_indexdef_string() without being adjusted correctly.

Reported-by: jian he <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxHwVPgeu8o9D8oUeDQYEHTAZGt-J5uaJNgYMzkAW7MiCA@mail.gmail.com

src/backend/utils/adt/ruleutils.c

@@ -1620,7 +1620,6 @@ pg_get_statisticsobjdef(PG_FUNCTION_ARGS)
 
 /*
  * Internal version for use by ALTER TABLE.
- * Includes a tablespace clause in the result.
  * Returns a palloc'd C string; no pretty-printing.
  */
 char *