rewrite scripts

try to provide better syntax and avoid using bash

debian/templates/image.prerm.in

@@ -1,17 +1,21 @@
-#!/bin/sh -e
+#!/bin/sh
+set -e
 
-version=@abiname@@localversion@
-image_path=/boot/@image-stem@-$version
+[ "$1" = remove ] || exit 0
 
-if [ "$1" != remove ]; then
-    exit 0
+version='@abiname@@localversion@'
+image_path="/boot/@image-stem@-${version}"
+
+if command -v linux-check-removal >/dev/null ; then
+    linux-check-removal "${version}"
 fi
 
-linux-check-removal $version
-
-if [ -d /etc/kernel/prerm.d ]; then
-    DEB_MAINT_PARAMS="$*" run-parts --report --exit-on-error --arg=$version \
-	      --arg=$image_path /etc/kernel/prerm.d
+if [ -d /etc/kernel/prerm.d ] ; then
+    DEB_MAINT_PARAMS="$*" \
+    run-parts --report --exit-on-error \
+      "--arg=${version}" \
+      "--arg=${image_path}" \
+    /etc/kernel/prerm.d
 fi
 
 exit 0