Avoid package qualification of $windows_os

Further fallout from commit 6ee26c6a4b. To keep code in sync and avoid
issues on older releases with different package names, simply use the
unqualified name like many other places in our code.

src/bin/pg_rewind/t/003_extrafiles.pl

@@ -82,7 +82,7 @@ sub run_test
 	# File::Find converts backslashes to slashes in the newer Perl
 	# versions. To support all Perl versions, do the same conversion
 	# for Windows before comparing the paths.
-	if ($PostgreSQL::Test::Utils::windows_os)
+	if ($windows_os)
 	{
 		for my $filename (@paths)
 		{