plpython: Adjust docs after removal of Python 2 support.

Reviewed-By: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/20211031184548.g4sxfe47n2kyi55r@alap3.anarazel.de

Author: anarazel

doc/src/sgml/hstore.sgml

@@ -943,12 +943,8 @@ ALTER TABLE tablename ALTER hstorecol TYPE hstore USING hstorecol || '';
    and <literal>hstore_plperlu</literal>, for trusted and untrusted PL/Perl.
    If you install these transforms and specify them when creating a
    function, <type>hstore</type> values are mapped to Perl hashes.  The
-   extensions for PL/Python are
-   called <literal>hstore_plpythonu</literal>, <literal>hstore_plpython2u</literal>,
-   and <literal>hstore_plpython3u</literal>
-   (see <xref linkend="plpython-python23"/> for the PL/Python naming
-   convention).  If you use them, <type>hstore</type> values are mapped to
-   Python dictionaries.
+   extension for PL/Python is called <literal>hstore_plpython3u</literal>.
+   If you use it, <type>hstore</type> values are mapped to Python dictionaries.
   </para>
 
   <caution>

doc/src/sgml/json.sgml

@@ -716,12 +716,9 @@ UPDATE table_name SET jsonb_field[1]['a'] = '1';
   </para>
 
   <para>
-   The extensions for PL/Python are called <literal>jsonb_plpythonu</literal>,
-   <literal>jsonb_plpython2u</literal>, and
-   <literal>jsonb_plpython3u</literal> (see <xref
-   linkend="plpython-python23"/> for the PL/Python naming convention).  If you
-   use them, <type>jsonb</type> values are mapped to Python dictionaries,
-   lists, and scalars, as appropriate.
+   The extension for PL/Python is called <literal>jsonb_plpython3u</literal>.
+   If you use it, <type>jsonb</type> values are mapped to Python
+   dictionaries, lists, and scalars, as appropriate.
   </para>
 
   <para>

doc/src/sgml/ltree.sgml

@@ -826,19 +826,15 @@ ltreetest=> SELECT ins_label(path,2,'Space') FROM test WHERE path <@ 'Top.
   <title>Transforms</title>
 
   <para>
-   Additional extensions are available that implement transforms for
-   the <type>ltree</type> type for PL/Python.  The extensions are
-   called <literal>ltree_plpythonu</literal>, <literal>ltree_plpython2u</literal>,
-   and <literal>ltree_plpython3u</literal>
-   (see <xref linkend="plpython-python23"/> for the PL/Python naming
-   convention).  If you install these transforms and specify them when
+   The <literal>ltree_plpython3u</literal> extension implements transforms for
+   the <type>ltree</type> type for PL/Python. If installed and specified when
    creating a function, <type>ltree</type> values are mapped to Python lists.
    (The reverse is currently not supported, however.)
   </para>
 
   <caution>
    <para>
-    It is strongly recommended that the transform extensions be installed in
+    It is strongly recommended that the transform extension be installed in
     the same schema as <filename>ltree</filename>.  Otherwise there are
     installation-time security hazards if a transform extension's schema
     contains objects defined by a hostile user.