[0156] Removed world drop chance for item 2203 and 2204

* Removed item 2203 (Brashclaw's Chopper) and item 2204 (Brashclaw's
Skewer) from reference_loot_template because they can only drop from
creature 506 (Sergeant Brashclaw)
Thanks to Neotmiren for pointing
Source: http://www.wowhead.com/item=2203
Source: http://www.wowhead.com/item=2204