doc: remove LC_COLLATE and LC_CTYPE from SHOW command

The corresponding read-only server settings have been removed since
in PG16. See commit b0f6c43716.

Author: Pierre Giraud <pierre.giraud@dalibo.com>
Discussion: https://www.postgresql.org/message-id/flat/a75a2fb0-f4b3-4c0c-be3d-7a62d266d760%40dalibo.com

doc/src/sgml/ref/show.sgml

@@ -77,30 +77,6 @@ SHOW ALL
         </listitem>
        </varlistentry>
 
-       <varlistentry>
-        <term><literal>LC_COLLATE</literal></term>
-        <listitem>
-         <para>
-          Shows the database's locale setting for collation (text
-          ordering).  At present, this parameter can be shown but not
-          set, because the setting is determined at database creation
-          time.
-         </para>
-        </listitem>
-       </varlistentry>
-
-       <varlistentry>
-        <term><literal>LC_CTYPE</literal></term>
-        <listitem>
-         <para>
-          Shows the database's locale setting for character
-          classification.  At present, this parameter can be shown but
-          not set, because the setting is determined at database creation
-          time.
-         </para>
-        </listitem>
-       </varlistentry>
-
        <varlistentry>
         <term><literal>IS_SUPERUSER</literal></term>
         <listitem>