Remove V1 grpc API.

[abizjak]

Purpose

Remove V1 API from the node.

Closes #1073

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[MilkywayPirate]

Looks good.

I think at some point we should rename all the "grpc2" stuff to simply being "grpc". There is now only one and only one grpc api of the node, so it could end up being a bit confusing the future having this "v2"..

[abizjak]

I think at some point we should rename all the "grpc2" stuff to simply being "grpc". There is now only one and only one grpc api of the node, so it could end up being a bit confusing the future having this "v2"..

I am not convinced this is a good idea. It'll be more confusing and disruptive to do renaming. It's fairly easy to remember we used to have some other API.