Remove archiso from ARM64 live package list

archiso is not in ALARM repos for aarch64 — pacstrap fails trying to
install it into the live ISO root. The Docker build environment already
has mkarchiso installed from source; the live ISO doesn't need it.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/docker/entrypoint-arm64.sh

@@ -22,7 +22,6 @@ base
 linux-aarch64
 linux-firmware
 mkinitcpio
-archiso
 grub
 efibootmgr
 xorg-server