Remove the multi-registry code

[arcanis]

Note: This is only a technical refactoring, we will still support custom registries, it doesn't affect anything from a feature set viewpoint.

The yarn registry being a mere mirror of the npm registry, this part of the code doesn't make sense. It also doesn't work since there's places where we make assumptions that we don't do in other places. The end result is something slower and more complex than needed.

[rally25rs]

Had this discussion externally with @BYK but IMO the yarn registry doesn't seem to add much value other than some metrics, and introduces another potential failure point (like today's CloudFlare issue). What do you think about just deprecating the yarn registry and pointing yarn v2 back to registry.npm.org directly? The yarn registry could of course be left up for a while for yarn v1 to use.

[arcanis]

Hey Jeff, this thread is specifically about the multi-registry code (ie config.registries), not about the indirection proxy. James opened a new thread to discuss this (#5891). It's a bit confusing because there's multiple contexts for the word registry 🙂

[5amo0os]

https://github.com/yarnpkg/yarn/projects/4#card-10030932