This was added long ago at this point to assist with caching, but caching has moved to a different level such that this wonky second level of a `Module` isn't necessary. This commit removes the `ModuleLocal` type to simplify accessors and generally make it easier to work with.
This is the wasmtime-obj crate, which contains an experimental prototype
for writing out native object files, using the wasm ABI defined by
wasmtime-environ.