Tests: backout process group creation (b01ae969181b).

This turns to be bad idea since hitting ^C no longer works as expected and
leaves daemons running.  And it's not used anyway.

lib/Test/Nginx.pm

diff --git a/lib/Test/Nginx.pm b/lib/Test/Nginx.pm
index c2a5aee..1e2884a 100644
--- a/lib/Test/Nginx.pm
+++ b/lib/Test/Nginx.pm
@@ -114,8 +114,7 @@
 
 	while ($self->{_daemons} && scalar @{$self->{_daemons}}) {
 		my $p = shift @{$self->{_daemons}};
-		# SIGTERM to process group
-		kill -15, $p;
+		kill 'TERM', $p;
 		wait;
 	}
 
@@ -155,7 +154,6 @@
 	die "Can't fork daemon: $!\n" unless defined $pid;
 
 	if ($pid == 0) {
-		setpgrp(0, 0);
 		if (ref($code) eq 'CODE') {
 			$code->(@args);
 			exit 0;