MDEV-13549 Wrong usage of mutex 'LOCK_wsrep_thd' and 'LOCK_thd_kill' test galera.MW-286

Test MW-286 occasionally failed with error the following message:

```
safe_mutex: Found wrong usage of mutex 'LOCK_wsrep_thd' and 'LOCK_thd_kill'
Mutex currently locked (in reverse order):
LOCK_thd_kill                     mariadb-server/sql/sql_class.h  line 3535
LOCK_wsrep_thd                    mariadb-server/sql/wsrep_thd.cc  line 88
```

The fix consists in calling thd->reset_killed() in wsrep_mysql_parse() after
LOCK_wsrep_thd is unlocked. Which avoids the taking locks LOCK_wsrep_thd and
LOCK_thd_kill in reverse order.

sql/sql_parse.cc

@@ -7193,7 +7193,6 @@ static void wsrep_mysql_parse(THD *thd, char *rawbuf, uint length,
           thd->wsrep_conflict_state == CERT_FAILURE)
       {
         thd->reset_for_next_command();
-        thd->reset_killed();
         if (is_autocommit                           &&
             thd->lex->sql_command != SQLCOM_SELECT  &&
             (thd->wsrep_retry_counter < thd->variables.wsrep_retry_autocommit))
@@ -7221,18 +7220,19 @@ static void wsrep_mysql_parse(THD *thd, char *rawbuf, uint length,
                       thd->thread_id, is_autocommit, thd->wsrep_retry_counter, 
                       thd->variables.wsrep_retry_autocommit, thd->query());
           my_error(ER_LOCK_DEADLOCK, MYF(0), "wsrep aborted transaction");
-          thd->reset_killed();
           thd->wsrep_conflict_state= NO_CONFLICT;
           if (thd->wsrep_conflict_state != REPLAYING)
             thd->wsrep_retry_counter= 0;             //  reset
         }
+        mysql_mutex_unlock(&thd->LOCK_wsrep_thd);
+        thd->reset_killed();
       }
       else
       {
         set_if_smaller(thd->wsrep_retry_counter, 0); // reset; eventually ok
-      }
         mysql_mutex_unlock(&thd->LOCK_wsrep_thd);
       }
+    }
 
     /* If retry is requested clean up explain structure */
     if (thd->wsrep_conflict_state == RETRY_AUTOCOMMIT && thd->lex->explain)