Get rid of adjust_appendrel_attr_needed(), which has been broken ever since

we extended the appendrel mechanism to support UNION ALL optimization.  The
reason nobody noticed was that we are not actually using attr_needed data for
appendrel children; hence it seems more reasonable to rip it out than fix it.
Back-patch to 8.2 because an Assert failure is possible in corner cases.
Per examination of an example from Jim Nasby.

In HEAD, also get rid of AppendRelInfo.col_mappings, which is quite inadequate
to represent UNION ALL situations; depend entirely on translated_vars instead.

src/include/optimizer/prep.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/optimizer/prep.h,v 1.62 2008/08/17 01:20:00 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/optimizer/prep.h,v 1.63 2008/11/11 18:13:32 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -51,9 +51,4 @@ extern void expand_inherited_tables(PlannerInfo *root);
 
 extern Node *adjust_appendrel_attrs(Node *node, AppendRelInfo *appinfo);
 
-extern Relids *adjust_appendrel_attr_needed(RelOptInfo *oldrel,
-							 AppendRelInfo *appinfo,
-							 AttrNumber new_min_attr,
-							 AttrNumber new_max_attr);
-
 #endif   /* PREP_H */