Remove subquery.

Author: bmomjian

doc/TODO

@@ -292,7 +292,6 @@ MISC
 * -Make oid use oidin/oidout not int4in/int4out in pg_type.h (Tom)
 * Improve Subplan list handling
 * Allow Subplans to use efficient joins(hash, merge) with upper variable
-  [subquery]
 * -use fmgr_info()/fmgr_faddr() instead of fmgr() calls in high-traffic
   places, like GROUP BY, UNIQUE, index processing, etc.
 * improve dynamic memory allocation by introducing tuple-context memory