stack/erp5: use repozo --kill-old-on-full when producing backups

from repozo doc:

> If a full backup is created, remove any prior full or incremental
> backup files (and associated metadata files) from the repository
> directory.

This solves a problem that after a pack some old repozo files were left
around, with this option they are automatically removed.

stack/erp5/buildout.hash.cfg

@@ -78,7 +78,7 @@ md5sum = 1333d2fc21f64da4010a4eafea59d141
 
 [template-zeo]
 filename = instance-zeo.cfg.in
-md5sum = 33075c3ab06613874b928d90e0c0006a
+md5sum = 702afb430227eebe4312a618da7ef7cb
 
 [template-zeo-conf]
 filename = zeo.conf.in

stack/erp5/instance-zeo.cfg.in

@@ -101,6 +101,7 @@ inline =
   echo "Backing up $storage_name ..."
   $repozo \
     --backup \
+    --kill-old-on-full \
     --gzip \
     --quick \
     --repository="$zodb_backup_directory/$storage_name" \