MDEV-10957: Assertion failure when dropping a myisam table with wsrep_replicate_myisam enabled

Internal updates to system statistical tables could wrongly
trigger an additional total-order replication if wsrep_repli
-cate_myisam is enabled.
Fixed by adding a check to skip total-order replication for
stat tables.

Test: galera.galera_var_replicate_myisam_on

sql/sql_statistics.h

@@ -107,6 +107,7 @@ double get_column_range_cardinality(Field *field,
                                     key_range *min_endp,
                                     key_range *max_endp,
                                     uint range_flag);
+bool is_stat_table(const char *db, const char *table);
 
 class Histogram
 {