doc: Remove reference to tty libpq connstring param

The tty connection string parameter was removed in commit 14d9b37
but the reference to it in the docs was mistakenly kept.  Fix by
removing it from the libpq documentation.  Backpatch through v14
where the parameter was removed.

Author: Noriyoshi Shinoda <noriyoshi.shinoda@hpe.com>
Discussion: https://postgr.es/m/DM4PR84MB173433216FCC2A3961879000EE6B9@DM4PR84MB1734.NAMPRD84.PROD.OUTLOOK.COM
Backpatch-through: 14

Author: danielgustafsson

doc/src/sgml/libpq.sgml

@@ -1388,15 +1388,6 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
       </listitem>
      </varlistentry>
 
-     <varlistentry id="libpq-connect-tty" xreflabel="tty">
-      <term><literal>tty</literal></term>
-      <listitem>
-      <para>
-       Ignored (formerly, this specified where to send server debug output).
-      </para>
-      </listitem>
-     </varlistentry>
-
      <varlistentry id="libpq-connect-replication" xreflabel="replication">
       <term><literal>replication</literal></term>
       <listitem>