Retire zpool_id infrastructure

In the interest of maintaining only one udev helper to give vdevs
user friendly names, the zpool_id and zpool_layout infrastructure
is being retired.  They are superseded by vdev_id which incorporates
all the previous functionality.

Documentation for the new vdev_id(8) helper and its configuration
file, vdev_id.conf(5), can be found in their respective man pages.
Several useful example files are installed under /etc/zfs/.

  /etc/zfs/vdev_id.conf.alias.example
  /etc/zfs/vdev_id.conf.multipath.example
  /etc/zfs/vdev_id.conf.sas_direct.example
  /etc/zfs/vdev_id.conf.sas_switch.example

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #981

configure.ac

@@ -98,9 +98,7 @@ AC_CONFIG_FILES([
 	cmd/zpios/Makefile
 	cmd/mount_zfs/Makefile
 	cmd/fsck_zfs/Makefile
-	cmd/zpool_layout/Makefile
 	cmd/zvol_id/Makefile
-	cmd/zpool_id/Makefile
 	cmd/vdev_id/Makefile
 	module/Makefile
 	module/avl/Makefile
@@ -119,7 +117,6 @@ AC_CONFIG_FILES([
 	scripts/zpios-profile/Makefile
 	scripts/zpios-test/Makefile
 	scripts/zpool-config/Makefile
-	scripts/zpool-layout/Makefile
 	scripts/common.sh
 	zfs.spec
 	zfs-modules.spec