Core/Player: Fix a query that was wrongly deleting items

CHAR_DEL_ITEM_INSTANCE deletes by item guid but in Player::DeleteFromDB the guid being used was player's guid.
That means that if player with guid 100 was deleted, the item with guid 100 would also be deleted. This item could or could not belong to the player.

Closes #8883
Closes #9136

Thanks to @vlad852 for finding the issue