actually... invoke only when $1 = upgrade

autoscripts/preinst-pycentral-clean

 # make sure python-central files are removed before new package is installed
-case "$1" in
-    install|upgrade)
-	if [ -f /var/lib/pycentral/#PACKAGE#.pkgremove ]
-	then
-		pycentral pkgremove #PACKAGE#
-		rm -f /var/lib/pycentral/#PACKAGE#.pkgremove
-	fi
-esac
+if [ "$1" = upgrade ] && [ -f /var/lib/pycentral/#PACKAGE#.pkgremove ]
+then
+	pycentral pkgremove #PACKAGE#
+	rm -f /var/lib/pycentral/#PACKAGE#.pkgremove
+fi