Deprecate bundled item data

[me4502]

This PR deprecates the concept of bundled item data, as well as the concept of "item material". This was added but never actually used. It's not very mod-compatible, and also requires storing increasingly large numbers of JSON files within the repo and jar files.

Due to the fact that WorldEdit never uses these at all, and that the bundled item registry is loaded when first accessed, this means we can remove the call to actually load it from WorldEdit. If something does happen to be using this deprecated API, it'll trigger it to be loaded upon first access.