Remove more unused module imports from TAP tests

This is a follow-up to commit 7dac61402 which removed a set of unused
modules from the TAP test.

The Config references in the pg_ctl and pg_rewind tests were removed
in commit 1c6d46293.  Fcntl ':mode' and File::stat in the pg_ctl test
were added in c37b3d08c which was probably a leftover from an earlier
version of the patch, as the function using these was added to another
module in that commit.

The Config reference in the ldap test was added in ee56c3b21 which in
turn use $^O instead of interrogating Config.

Author: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Discussion: https://postgr.es/m/87lewyqk45.fsf@wibble.ilmari.org

src/bin/pg_ctl/t/001_start_stop.pl

@@ -4,9 +4,6 @@
 use strict;
 use warnings;
 
-use Config;
-use Fcntl ':mode';
-use File::stat qw{lstat};
 use PostgreSQL::Test::Cluster;
 use PostgreSQL::Test::Utils;
 use Test::More;

src/bin/pg_rewind/t/RewindTest.pm

@@ -35,7 +35,6 @@ use strict;
 use warnings;
 
 use Carp;
-use Config;
 use Exporter 'import';
 use File::Copy;
 use File::Path qw(rmtree);

src/test/ldap/t/001_auth.pl

@@ -6,7 +6,6 @@ use warnings;
 use PostgreSQL::Test::Utils;
 use PostgreSQL::Test::Cluster;
 use Test::More;
-use Config;
 
 
 my ($slapd, $ldap_bin_dir, $ldap_schema_dir);