libzpool: remove global libzpool includes

Only include the zfs headers where they're currently required to
compile.  Unfortunately, including zfs_ioctl.h in user space pulls
in a bunch of internal zfs headers as a side effect.  We'll need
to move these structures in to a new shared header to avoid this.
We should not need to add the LIBZPOOL_CPPFLAGS when building the
zed, zinject, zpool, libzfs, ior libzfs_core.

Sponsored-by: https://despairlabs.com/sponsor/
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #17861

lib/libspl/taskq.c

@@ -29,7 +29,12 @@
  * Copyright (c) 2014 by Delphix. All rights reserved.
  */
 
-#include <sys/zfs_context.h>
+#include <sys/sysmacros.h>
+#include <sys/timer.h>
+#include <sys/types.h>
+#include <sys/thread.h>
+#include <sys/taskq.h>
+#include <sys/kmem.h>
 
 int taskq_now;
 taskq_t *system_taskq;

lib/libzfs/libzfs_crypto.c

@@ -19,7 +19,6 @@
  * Copyright 2020 Joyent, Inc.
  */
 
-#include <sys/zfs_context.h>
 #include <sys/fs/zfs.h>
 #include <sys/dsl_crypt.h>
 #include <libintl.h>

lib/libzpool/Makefile.am

@@ -4,7 +4,6 @@ libzpool_la_CFLAGS  = $(AM_CFLAGS) $(KERNEL_CFLAGS) $(LIBRARY_CFLAGS)
 libzpool_la_CFLAGS += $(ZLIB_CFLAGS)
 
 libzpool_la_CPPFLAGS  = $(AM_CPPFLAGS) $(LIBZPOOL_CPPFLAGS)
-libzpool_la_CPPFLAGS += -I$(srcdir)/include/os/@ac_system_l@/zfs
 libzpool_la_CPPFLAGS += -DLIB_ZPOOL_BUILD
 
 lib_LTLIBRARIES += libzpool.la