debian_version: Force-remove the symlink

Change-Id: I1c7bae062e6aa4620be9cc60a1f5599136742e05
diff --git a/debian/preinst b/debian/preinst
new file mode 100755
index 0000000..f039f7b
--- /dev/null
+++ b/debian/preinst
@@ -0,0 +1,7 @@
+#!/bin/sh
+set -e
+
+if [ -L /etc/debian_version ]; then
+    rm -f /etc/debian_version
+fi
+