the intent of these hacks was to break cyclic references to avoid having objects lingering in memory. However, all of the stuff that's being removed in this commit no longer has any effect anyway, due to the fact that these things don't circularly reference each other anymore. Notably, Tile inventories now keep Position instead of a Tile ref.
this allows multiple problems to be solved:
1) Cycle between tile and inventory is now removed.
2) BlockInventory now provides a consistent API for plugins to get the block holding an inventory.
