NixOS Root on ZFS: Do not bind mount /boot/efi

Previously we used a bind mount from /boot/efis/*-part1
to /boot/efi to facilitate bootloader configuration.
Recent reports indicate that this bind mount prevents
the system from booting.  This pull request removes the
bind mount.

Closes #383.

Signed-off-by: Maurice Zhou <ja@apvc.uk>

docs/Getting Started/NixOS/Root on ZFS/2-system-installation.rst

@@ -128,6 +128,3 @@ System Installation
      mkdir -p /mnt/boot/efis/${i##*/}-part1
      mount -t vfat ${i}-part1 /mnt/boot/efis/${i##*/}-part1
     done
-
-    mkdir -p /mnt/boot/efi
-    mount -t vfat $(echo $DISK | cut -f1 -d\ )-part1 /mnt/boot/efi