Drop vanilla GetItemInfo shim for C_Item.GetItemInfo

The compat/vanilla.lua GetItemInfo override reshaped vanilla's tuple into
retail order by inserting nil at slot 4 (itemLevel), but truncated at 8
fields, dropping itemEquipLoc/itemTexture. ClassicAPI's global GetItemInfo
keeps the vanilla shape (its hook only warms the item cache), so the shim
stayed necessary but incomplete.

Remove it and point the three callers at ClassicAPI's C_Item.GetItemInfo,
which returns the full 18-field retail tuple. Positions 1-8 are identical
to the old shim output, so bags/roll are unchanged; character.lua's
itemSlot (equipLoc, field 9) was always nil under the truncating shim and
now resolves correctly for ShaguScore.

compat/vanilla.lua

@@ -29,15 +29,6 @@ UNITFRAME_SECURE_TEMPLATE = nil
 
 --[[ Vanilla API Extensions ]]--
 
-do -- GetItemInfo
-  local name, link, rarity, minlevel, itype, isubtype, stack
-  function GetItemInfo(item)
-    if not item then return end
-    name, link, rarity, minlevel, itype, isubtype, stack = _G.GetItemInfo(item)
-    return name, link, rarity, nil, minlevel, itype, isubtype, stack
-  end
-end
-
 do -- RunMacroText
   local obj = { ["GetText"] = function(self) return self.text end }
   obj = setmetatable(obj, {__index = function(tab,key)