dkio: remove kernel dkio.h compatibility header

Without DKIOCFLUSHWRITECACHE, we no longer need the compat header. Note
that we're keeping the userspace SPL compat header, which is used by
libefi.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #16064

include/os/linux/spl/sys/dkio.h

@@ -1,39 +0,0 @@
-/*
- *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
- *  Copyright (C) 2007 The Regents of the University of California.
- *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
- *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
- *  UCRL-CODE-235197
- *
- *  This file is part of the SPL, Solaris Porting Layer.
- *
- *  The SPL is free software; you can redistribute it and/or modify it
- *  under the terms of the GNU General Public License as published by the
- *  Free Software Foundation; either version 2 of the License, or (at your
- *  option) any later version.
- *
- *  The SPL is distributed in the hope that it will be useful, but WITHOUT
- *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
- *  for more details.
- *
- *  You should have received a copy of the GNU General Public License along
- *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#ifndef _SPL_DKIO_H
-#define	_SPL_DKIO_H
-
-#define	DFL_SZ(num_exts) \
-	(sizeof (dkioc_free_list_t) + (num_exts - 1) * 16)
-
-#define	DKIOC		(0x04 << 8)
-#define	DKIOCFLUSHWRITECACHE	(DKIOC|34)	/* flush cache to phys medium */
-
-/*
- * ioctl to free space (e.g. SCSI UNMAP) off a disk.
- * Pass a dkioc_free_list_t containing a list of extents to be freed.
- */
-#define	DKIOCFREE	(DKIOC|50)
-
-#endif /* _SPL_DKIO_H */