Remove build environment artefact from Debian package.

(Redmine issue: #7379)

packaging/debian/rules

@@ -26,6 +26,8 @@ binary:
 	cp -r ../etc/init.d debian/mentat-ng/etc/
 	cp -r ../etc/systemd debian/mentat-ng/etc/
 
+	if [ -L 'debian/mentat-ng/etc/mentat/migrations-events/.env' ]; then rm -f 'debian/mentat-ng/etc/mentat/migrations-events/.env'; fi
+
 ifeq ($(BUILD_SUITE),production)
 	echo "mentat-ng" > debian/mentat-ng/etc/mentat/install.pip
 else ifeq ($(BUILD_SUITE),release)