Minor code cleanup

The D3 can now access the modded items when selecting what to remove. HOORAY

Fixed an RNG issue occurring when the number of removable items was exactly two.

The D3 can now remove the modded items in the first booster pack. If you're using other mods, you can add the items' IDs to the "very removable IDs" parameter, and they'll be added to The D3's "I can remove this" list.

Updated "do not remove" list to include all items that The D4 etc. skip when rerolling your character (Halo of Flies, Dead Cat, Polaroid, MissingNo, et cetera). This also means that players can add items to be skipped, by editing the "unremovable ids" parameter!

The D3 no longer removes key pieces if you're on a Challenge. This includes Challenges that are added by other mods! Dive for Mega Satan safe in the knowledge that you'll be able to open the door when you get there.

Fixed an issue with the item pools.

Updated itempools.xml so the D3 is pulled by name, rather than by ID. Also fixed DecreaseBy in the Treasure pool to match that of The D6.

Stopped the D3 from stealing your Restock when you're in Greed Mode or Greedier Mode. WHEW!

Added a custom item ID to avoid conflicts with other mods