Remove backwards-compatible run_config from execution context (#1874)
Started this for https://github.com/dagster-io/dagster/issues/1874 - seems like one thing to resolve is whether create_execution_plan should take a RunConfig or a PipelineRun as an argument, which I guess depends on how much we consider this a user-facing API?
There's a bit of both in this diff, would love to discuss and we can pick one and I'll follow-up here.
Test Plan: unit
Reviewed By: prha
Differential Revision: https://dagster.phacility.com/D1986