configs/releng/airootfs/etc/mkinitcpio.conf: remove archiso_shutdown

The archiso_shutdown hook has been obsolete since mkinitcpio 16.
https://lists.archlinux.org/pipermail/arch-dev-public/2013-December/025742.html

Related to mkinitcpio/mkinitcpio-archiso#8.

configs/releng/airootfs/etc/mkinitcpio.conf

@@ -49,7 +49,7 @@ FILES=()
 #
 ##   NOTE: If you have /usr on a separate partition, you MUST include the
 #    usr, fsck and shutdown hooks.
-HOOKS=(base udev modconf memdisk archiso_shutdown archiso archiso_loop_mnt archiso_pxe_common archiso_pxe_nbd archiso_pxe_http archiso_pxe_nfs archiso_kms block filesystems keyboard)
+HOOKS=(base udev modconf memdisk archiso archiso_loop_mnt archiso_pxe_common archiso_pxe_nbd archiso_pxe_http archiso_pxe_nfs archiso_kms block filesystems keyboard)
 
 # COMPRESSION
 # Use this to compress the initramfs image. By default, gzip compression