Remove unneeded header from libzpool/kernel.c

The sys/signal.h header doesn't exist on FreeBSD, nor is
it needed on Linux.

Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matt Macy <mmacy@FreeBSD.org>
Closes #9510

lib/libspl/include/sys/signal.h

@@ -1,35 +0,0 @@
-/*
- * CDDL HEADER START
- *
- * The contents of this file are subject to the terms of the
- * Common Development and Distribution License, Version 1.0 only
- * (the "License").  You may not use this file except in compliance
- * with the License.
- *
- * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
- * or http://www.opensolaris.org/os/licensing.
- * See the License for the specific language governing permissions
- * and limitations under the License.
- *
- * When distributing Covered Code, include this CDDL HEADER in each
- * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
- * If applicable, add the following below this CDDL HEADER, with the
- * fields enclosed by brackets "[]" replaced with your own identifying
- * information: Portions Copyright [yyyy] [name of copyright owner]
- *
- * CDDL HEADER END
- */
-/*
- * Copyright 2017 Zettabyte Software, LLC.  All rights reserved.
- * Use is subject to license terms.
- */
-
-/*
- * Compiling against musl correctly points out that including sys/signal.h is
- * disallowed by the Single UNIX Specification when building in userspace, so
- * we implement a dummy header to redirect the include to the proper header.
- */
-#ifndef _LIBSPL_SYS_SIGNAL_H
-#define	_LIBSPL_SYS_SIGNAL_H
-#include <signal.h>
-#endif /* _LIBSPL_SYS_SIGNAL_H */

lib/libzpool/kernel.c

@@ -32,7 +32,6 @@
 #include <string.h>
 #include <zlib.h>
 #include <libgen.h>
-#include <sys/signal.h>
 #include <sys/spa.h>
 #include <sys/stat.h>
 #include <sys/processor.h>