Remove fragments in before rollback for streaming transactions

which got BF aborted in total order.

include/wsrep/storage_service.hpp

@@ -55,6 +55,12 @@ namespace wsrep
          */
         virtual int update_fragment_meta(const wsrep::ws_meta&) = 0;
 
+        /**
+         * Remove fragments from storage. The storage service must have
+         * adopted a transaction prior this call.
+         */
+        virtual int remove_fragments() = 0;
+
         /**
          * Commit the transaction.
          */