packaging: cleanup() did not read the value of $CLEANUP When the original author put CLEANUP in a conditional statement he was probably willing to use it to control the "if". This change tries to restore that behaviour: the "rm" clause is triggered if and only if CLEANUP is defined and not empty.

--- a/contrib/packaging/builddeb	Tue Oct 09 22:18:35 2018 +0200
+++ b/contrib/packaging/builddeb	Tue Oct 09 22:24:38 2018 +0200
@@ -15,7 +15,7 @@
 DEBFLAGS=-b
 
 cleanup() {
-    if [ '$CLEANUP' ]; then
+    if [ "$CLEANUP" ]; then
         rm -r "$PWD/debian";
     fi
 }