Changes to vending machine prices

I changed the prices of the items in the vending machine spawn list to better reflect reality. I also removed the price of most prepackaged food containers ( the prize of the container and of the contained item added when calculating the final prize; while that makes sense when trading with other people, it makes no sense for a machine to be programmed that way, and as said in #6482 the json prizes are precataclysm, plus most of those containers are technically junk).

I also removed or changed this entries from the spawn list
-Milk, because well a vending machine selling milk in gallon jugs is pretty strange
-Chips2, their description said they were own-brand so it should be pretty rare for a vending machine to sell those
-Replaced popcorn kernels with popcorn.