1. Include the builtin-actors in the lotus source tree.
2. Embed the bundle on build instead of downloading at runtime.
3. Avoid reading the bundle whenever possible by including bundle
   metadata (the bundle CID, the actor CIDs, etc.).
4. Remove everything related to dependency injection.
    1. We're no longer downloading the bundle, so doing anything ahead
       of time doesn't really help.
    2. We register the manifests on init because, unfortunately, they're
       global.
    3. We explicitly load the current actors bundle in the genesis
       state-tree method.
    4. For testing, we just change the in-use bundle with a bit of a
       hack. It's not great, but using dependency injection doesn't make
       any sense either because, again, the manifest information is
       global.

fixes #8701

Instead, we override bundles using environment variables and overrides
in the build parameter files.

1. Use mockProofs to determine the correct test bundle.
2. Don't even bother setting InsecurePoStValidation for itests, it's
already set.

This gets tested:

1. When we load dynamically (by path) specified bundles.
2. When we decode the embedded bundles to generate the metadata.

Effectively, this lets us test that the embedded bundles are actually
correct.