The manual partitioning setup was already requiring the user to check
the ESP flag for the EFI System Partition. Now the autopartitioning also
sets it directly (a one-line change). The sgdisk call in the bootloader
module is thus no longer necessary (it was only a workaround because
kpmcore < 2.1.0 did not support FlagEsp), so remove that snippet.
This fixes configurations such as NVME disks where splitting boot_device
into boot_device[-1:] and boot_device[:-1] is not the correct split
(because the partition gets a 2-letter suffix) (reported by demmm on
IRC).
