as/external/internal.pb.go points to wrong path prefix

[bconway]

Compare:

https://github.com/brocaar/chirpstack-api/blob/master/go/as/external/internal.pb.go#L695

to

https://github.com/brocaar/chirpstack-application-server/blob/master/api/internal.pb.go#L690

This results in errors like the following:

"rpc error: code = Unimplemented desc = unknown service external.InternalService"

[brocaar]

Good spot 👍 you're right, I will move the proto definitions under as/external/api that should solve the prefix issue.