Remove extra kernel install script

An initramfs post-update script called `systemd-boot` has been added to
systemd that performs the same function as `zz_kernel-install`, which
appears to be an Apertis addition. Remove this as we don't need it
anymore.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

debian/extra/zz_kernel-install

-#!/bin/sh
-
-case "$DPKG_MAINTSCRIPT_PACKAGE" in
-    linux-image-*)
-        exit 0
-        ;;
-    *)
-        kernel-install add "$1"
-        ;;
-esac

debian/systemd-boot.install

@@ -9,4 +9,3 @@ usr/share/bash-completion/completions/bootctl
 ../extra/initramfs etc/
 ../extra/kernel etc/
 ../extra/kernel-install.d/* usr/lib/kernel/install.d
-../extra/zz_kernel-install etc/initramfs/post-update.d