Fix duplicated index entry in doc.

Commit cfe96ae corrected the name of pg_logical_emit_message()
in its index entry. But this typo fix caused duplicated index
entry because there was another index entry for the function.

Spotted by Tom Lane.

doc/src/sgml/func.sgml

@@ -18414,9 +18414,6 @@ postgres=# SELECT * FROM pg_xlogfile_name_offset(pg_stop_backup());
 
       <row>
        <entry id="pg-logical-emit-message-bytea">
-        <indexterm>
-         <primary>pg_logical_emit_message</primary>
-        </indexterm>
         <literal><function>pg_logical_emit_message(<parameter>transactional</parameter> <type>bool</type>, <parameter>prefix</parameter> <type>text</type>, <parameter>content</parameter> <type>bytea</type>)</function></literal>
        </entry>
        <entry>