Remove changing the item type during game

When one walks around and some item gets randomly spawned and that item spoils, but has the can_food container (example: broth), the (removed) code would set the spoils property of broth to 0.

This means any already existing broth would be unrotten (because the game check the rotten/fresh state only for food that *can* rot). That would of cause apply to any broth, be it in can_food or self-made by the player. Even those liquid items on the ground.

It resets when the game is reloaded because the json entry of broth says it spoils in 160 units (hours was it?).

So upon reload the broth is suddenly rotten again. Then one walks around, new broth gets spawned and all the broth is unrotten again!

Fixes #2643, but of course not the whole rotten food system.

This https://github.com/CleverRaven/Cataclysm-DDA/issues/2643#issuecomment-29544770 is related to the automatically merging of liquids/stacks and not directly related to rotting.