Fixes #2026
The ARM64 left the vendor directory in an inconsistent state, go1.13 doesn't care so we didn't catch it but go1.14 does.
We forgot to run typecheckrpc.go periodically and it didn't work anymore and there were some minor errors in service/rpc2/client.go. Rewrite typecheckrpc.go using go/packages, so that it works with go1.11 and go.mod, and fix the issues in client.go