Followup fix for 2708f441

Thanks: Patrick Schleizer <adrelanos@whonix.org> for spotting and reporting
Closes: https://github.com/grml/grml-debootstrap/issues/256

change from EFI to ESP for arm64 builds

instead of sometimes mixed with "${MNTPOINT}/boot/efi"

because no longer provided by Debian

to work around an issue by github actions
drop `-q` from modprobe for better debug output

because it will not always work

will not work in cases where /dev etc is still mounted inside the chroot

because the cleanup function gets run by the error handler and should
not be nested

https://github.com/grml/grml-debootstrap/issues/224#issuecomment-1779673194

because these are now covered by the new error handling method

only delete `$MNTPOINT` if such a folder actually exists

only delete `$MNTPOINT` if such a folder actually exists

No need to use both, `eend 1` and `bailout 1`.
In these cases, only `bailout 1` is sufficient.

because these are now covered by the error_handler

busybox is useful for debugging initramfs issues, though it's not
necessary by default. Also tools like cryptsetup which rely on busybox
in initramfs stage have busybox as dependency anyways.

Thanks: Patrick Schleizer + Chris Hofstaedtler
Closes: https://github.com/grml/grml-debootstrap/issues/240

fixes https://github.com/grml/grml-debootstrap/issues/235