scripts/mkimg.standard.sh: ..actually, remove xz

busybox unxz works for decompressing arbitrary xz archives- no need for
the full tool.

saves 0.4MB from the prior change

scripts/mkimg.standard.sh

@@ -58,7 +58,7 @@ profile_extended() {
 		btrfs-progs cksfv dosfstools cryptsetup
 		e2fsprogs e2fsprogs-extra efibootmgr f2fs-tools
 		grub-bios grub-efi lvm2 lz4 mdadm mkinitfs mtools nfs-utils
-		parted rsync sfdisk syslinux util-linux xfsprogs xz zstd zfs
+		parted rsync sfdisk syslinux util-linux xfsprogs zstd zfs
 		"
 
 	local _k _a