Remove one memoize test case added by commit 069d0ff02.

This test case turns out to depend on the assumption that a non-Var
subquery output that's underneath an outer join will always get
wrapped in a PlaceHolderVar.  But that behavior causes performance
regressions in some cases compared to what happened before v16.
The next commit will avoid inserting a PHV in the same cases where
pre-v16 did, and that causes get_memoized_path to not detect that
a memoize plan could be used.

Commit this separately, in hopes that we can restore the test after
making get_memoized_path smarter.  (It's failing to find memoize
plans in adjacent cases where no PHV was ever inserted, so there
is definitely room for improvement there.)

Discussion: https://postgr.es/m/CAG1ps1xvnTZceKK24OUfMKLPvDP2vjT-d+F2AOCWbw_v3KeEgg@mail.gmail.com

src/test/regress/expected/memoize.out

@@ -160,36 +160,6 @@ WHERE s.c1 = s.c2 AND t1.unique1 < 1000;
   1000 | 9.5000000000000000
 (1 row)
 
--- Try with LATERAL references within PlaceHolderVars
-SELECT explain_memoize('
-SELECT COUNT(*), AVG(t1.twenty) FROM tenk1 t1 LEFT JOIN
-LATERAL (SELECT t1.two+t2.two AS c1, t2.unique1 AS c2 FROM tenk1 t2) s ON TRUE
-WHERE s.c1 = s.c2 AND t1.unique1 < 1000;', false);
-                                   explain_memoize                                    
---------------------------------------------------------------------------------------
- Aggregate (actual rows=1 loops=N)
-   ->  Nested Loop (actual rows=1000 loops=N)
-         ->  Seq Scan on tenk1 t1 (actual rows=1000 loops=N)
-               Filter: (unique1 < 1000)
-               Rows Removed by Filter: 9000
-         ->  Memoize (actual rows=1 loops=N)
-               Cache Key: t1.two
-               Cache Mode: binary
-               Hits: 998  Misses: 2  Evictions: Zero  Overflows: 0  Memory Usage: NkB
-               ->  Seq Scan on tenk1 t2 (actual rows=1 loops=N)
-                     Filter: ((t1.two + two) = unique1)
-                     Rows Removed by Filter: 9999
-(12 rows)
-
--- And check we get the expected results.
-SELECT COUNT(*), AVG(t1.twenty) FROM tenk1 t1 LEFT JOIN
-LATERAL (SELECT t1.two+t2.two AS c1, t2.unique1 AS c2 FROM tenk1 t2) s ON TRUE
-WHERE s.c1 = s.c2 AND t1.unique1 < 1000;
- count |        avg         
--------+--------------------
-  1000 | 9.0000000000000000
-(1 row)
-
 -- Ensure we do not omit the cache keys from PlaceHolderVars
 SELECT explain_memoize('
 SELECT COUNT(*), AVG(t1.twenty) FROM tenk1 t1 LEFT JOIN

src/test/regress/sql/memoize.sql

@@ -85,17 +85,6 @@ SELECT COUNT(*), AVG(t1.twenty) FROM tenk1 t1 LEFT JOIN
 LATERAL (SELECT t1.two+1 AS c1, t2.unique1 AS c2 FROM tenk1 t2) s ON TRUE
 WHERE s.c1 = s.c2 AND t1.unique1 < 1000;
 
--- Try with LATERAL references within PlaceHolderVars
-SELECT explain_memoize('
-SELECT COUNT(*), AVG(t1.twenty) FROM tenk1 t1 LEFT JOIN
-LATERAL (SELECT t1.two+t2.two AS c1, t2.unique1 AS c2 FROM tenk1 t2) s ON TRUE
-WHERE s.c1 = s.c2 AND t1.unique1 < 1000;', false);
-
--- And check we get the expected results.
-SELECT COUNT(*), AVG(t1.twenty) FROM tenk1 t1 LEFT JOIN
-LATERAL (SELECT t1.two+t2.two AS c1, t2.unique1 AS c2 FROM tenk1 t2) s ON TRUE
-WHERE s.c1 = s.c2 AND t1.unique1 < 1000;
-
 -- Ensure we do not omit the cache keys from PlaceHolderVars
 SELECT explain_memoize('
 SELECT COUNT(*), AVG(t1.twenty) FROM tenk1 t1 LEFT JOIN