scripts/prune-kernel: Use kernel-install if available

If the new-kernel-pkg utility isn't present, try using kernel-install.
This is what the %preun scriptlet in scripts/package/mkspec does too.

Signed-off-by: Reza Arbab <[e-mail]>
Signed-off-by: Masahiro Yamada <[e-mail]>

scripts/prune-kernel

···
                 rm -f "/boot/initramfs-$f.img" "/boot/System.map-$f"
                 rm -f "/boot/vmlinuz-$f"   "/boot/config-$f"
                 rm -rf "/lib/modules/$f"
-                new-kernel-pkg --remove $f
+                if [ -x "$(command -v new-kernel-pkg)" ]; then
+                        new-kernel-pkg --remove $f
+                elif [ -x "$(command -v kernel-install)" ]; then
+                        kernel-install remove $f
+                fi
         fi
 done