Fix wrong description of BackgroundPsql's timeout.

Backpatch through 16 where this was introduced by 664d757531.

Reviewed-by: Daniel Gustafsson
Backpatch-through: 16
Discussion: http://postgr.es/m/CAD21AoBXMEqDBLoDuAWVWoTLYB4aNsxx4oYNmyJJbhfq_vGQBQ@mail.gmail.com

src/test/perl/PostgreSQL/Test/Cluster.pm

@@ -1972,8 +1972,7 @@ sub psql
 
 Invoke B<psql> on B<$dbname> and return a BackgroundPsql object.
 
-A default timeout of $PostgreSQL::Test::Utils::timeout_default is set up,
-which can be modified later.
+A timeout of $PostgreSQL::Test::Utils::timeout_default is set up.
 
 psql is invoked in tuples-only unaligned mode with reading of B<.psqlrc>
 disabled.  That may be overridden by passing extra psql parameters.
@@ -2039,8 +2038,7 @@ sub background_psql
 Invoke B<psql> on B<$dbname> and return a BackgroundPsql object, which the
 caller may use to send interactive input to B<psql>.
 
-A default timeout of $PostgreSQL::Test::Utils::timeout_default is set up,
-which can be modified later.
+A timeout of $PostgreSQL::Test::Utils::timeout_default is set up.
 
 psql is invoked in tuples-only unaligned mode with reading of B<.psqlrc>
 disabled.  That may be overridden by passing extra psql parameters.