[PG15 Doc] remove "tty" connect string from manual

Hello, hackers.

As of PostgreSQL 14, "tty" in the libpq connection string has already been removed with the commit below.
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=14d9b37607ad30c3848ea0f2955a78436eff1268

But https://www.postgresql.org/docs/15/libpq-connect.html#LIBPQ-CONNSTRING still says "Ignored (formerly, this
specifiedwhere to send server debug output)". The attached patch removes the "tty" item. 

Regards,
Noriyoshi Shinoda