Doc: update old reference to "result cache"

During the PostgreSQL 14 cycle, the Memoize executor node was briefly
called "Result Cache" until it was renamed in 83f4fcc.  That commit
missed one reference.

Reported-by: Paul A Jungwirth
Packpatch-through: 14, where Memoize was added
Discussion: https://postgr.es/m/CA+renyX=40YXhsfPTzn13oNOPO3TJ12CK9GX-2P2pvnQiScefA@mail.gmail.com

Author: david-rowley

doc/src/sgml/config.sgml

@@ -1891,9 +1891,8 @@ include_dir 'conf.d'
         fact in mind when choosing the value.  Sort operations are used
         for <literal>ORDER BY</literal>, <literal>DISTINCT</literal>,
         and merge joins.
-        Hash tables are used in hash joins, hash-based aggregation, result
-        cache nodes and hash-based processing of <literal>IN</literal>
-        subqueries.
+        Hash tables are used in hash joins, hash-based aggregation, memoize
+        nodes and hash-based processing of <literal>IN</literal> subqueries.
        </para>
        <para>
         Hash-based operations are generally more sensitive to memory