Don't listen to localhost in ssl_passphrase_callback test

Commit 896fcdb230 contained an unnecessary setting that listened to
localhost. Since the test doesn't actually try to make an SSL connection
to the database this isn't required. Moreover, it's a security hole.

Per gripe from Tom Lane.

src/test/modules/ssl_passphrase_callback/t/001_testfunc.pl

@@ -28,7 +28,6 @@ $node->append_conf('postgresql.conf',
 	"ssl_passphrase.passphrase = '$rot13pass'");
 $node->append_conf('postgresql.conf',
 	"shared_preload_libraries = 'ssl_passphrase_func'");
-$node->append_conf('postgresql.conf', "listen_addresses = 'localhost'");
 $node->append_conf('postgresql.conf', "ssl = 'on'");
 
 my $ddir = $node->data_dir;