Creature/Misc: fix blue-and-white cube thrown by Dragonflayer Strategists

Closes #20502

sql/updates/world/3.3.5/2017_10_02_03_world.sql

@@ -0,0 +1,7 @@
+-- 
+UPDATE `creature_equip_template` SET `ItemID3`=29010 WHERE `CreatureID`=23956;
+
+DELETE FROM `spell_custom_attr` WHERE `entry` IN (42772, 59685);
+INSERT INTO `spell_custom_attr` (`entry`,`attributes`) VALUES
+(42772, 0x80000),
+(59685, 0x80000);