efiboot.img is bloated

The ISO includes the kernel and initramfs twice. Once in ISO 9660, and again in FAT (efiboot.img).

This is because systemd-boot doesn't have file system drivers, so it cannot load the kernel and initramfs from the ISO 9660 volume.

Since the releng initramfs image is huge (~45 MiB), the ISO is wasting a lot of space.

Possible solutions are:

• Replace systemd-boot with a boot loader that has a driver for ISO 9660.
• Find some way to reduce the initramfs size.
• Wait for systemd issue 15617 to get implemented, set the ISO 9660 volume as an Extended Boot Loader Partition and place an ISO 9660 EFI driver in efiboot.img. After !160 (merged), -iso_mbr_part_type can't set the ISO partition type anymore.