Clarify DROP EXTENSION docs regarding explicitly dependent routines

Per suggestion from Robert Haas

Backpatch to v14

Discussion: https://www.postgresql.org/message-id/CA%2BTgmoZ1QvHquYHLkMy1oHKqz4-E7QQctj6e0ocq_GP1B5%2B9bA%40mail.gmail.com

doc/src/sgml/ref/drop_extension.sgml

@@ -32,7 +32,8 @@ DROP EXTENSION [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [
    <command>DROP EXTENSION</command> removes extensions from the database.
    Dropping an extension causes its component objects, and other explicitly
    dependent routines (see <xref linkend="sql-alterroutine"/>,
-   the depends on extension action), to be dropped as well.
+   the <literal>DEPENDS ON EXTENSION <replaceable>extension_name</replaceable>
+   </literal> action), to be dropped as well.
   </para>
 
   <para>