Remove AutoFlow

[jc-harrison]

The AutoFlow component of FlowKit has been around for a while, but has had little active use. We are now looking to replace AutoFlow with tools for running FlowKit-connected notebooks using Airflow (e.g. an existing Airflow instance that's running FlowETL).

AutoFlow has Ruby dependencies, unlike any other FlowKit components, which incurs additional maintenance effort. My feeling is that it's no longer worth keeping the AutoFlow code around in this repo.