Remove duplicate (and now incorrect) documentation for row-wise IS [NOT]

NULL.  Noted by Teodor.

doc/src/sgml/func.sgml

-<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.341 2006/09/28 20:51:41 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.342 2006/09/29 18:36:45 tgl Exp $ -->
 
  <chapter id="functions">
   <title>Functions and Operators</title>
@@ -8829,14 +8829,6 @@ SELECT col1 FROM tab1
    <primary>IS NOT DISTINCT FROM</primary>
   </indexterm>
 
-  <indexterm>
-   <primary>IS NULL</primary>
-  </indexterm>
-
-  <indexterm>
-   <primary>IS NOT NULL</primary>
-  </indexterm>
-
   <para>
    This section describes several specialized constructs for making
    multiple comparisons between groups of values.  These forms are
@@ -9072,16 +9064,6 @@ AND
    be either true or false, never null.
   </para>
 
-<synopsis>
-<replaceable>row_constructor</replaceable> IS NULL
-<replaceable>row_constructor</replaceable> IS NOT NULL
-</synopsis>
-
-  <para>
-   These constructs test a row value for null or not null.  A row value
-   is considered not null if it has at least one field that is not null.
-  </para>
-
   </sect2>
  </sect1>