MDEV#6098 mysqldump sst fails on maria-10.0-galera

* Removed the unnecessary call to wsrep_cleanup_progress_file,
  which was returning code 1 and eventually causing SST to fail.
* Also initialized the unused WSREP_SST_OPT_CONF to avoid error
  message.

scripts/wsrep_sst_mysqldump.sh

@@ -17,6 +17,10 @@
 
 # This is a reference script for mysqldump-based state snapshot tansfer
 
+# This variable is not used in mysqldump sst, so better initialize it
+# to avoid shell's "parameter not set" message.
+WSREP_SST_OPT_CONF=""
+
 . $(dirname $0)/wsrep_sst_common
 
 EINVAL=22
@@ -119,5 +123,4 @@ else
     wsrep_log_info "Bypassing state dump."
     echo $SET_START_POSITION | $MYSQL
 fi
-wsrep_cleanup_progress_file
-#
+