[dagit] Fix left nav schedules/sensors filtering
Looks like an oversight with repo filtering in the left nav. Schedules and sensors aren't being correctly filtered down to the active repos.
We can just use the repos list and filter down to any active items.
Test Plan: Load a workspace with multiple repositories, run Dagit. Change left nav filters to view one repo, the other, both, and neither. Verify that in each situation, the schedules/sensors section filters to the correct list.
Reviewers: bengotow, prha
Reviewed By: prha
Differential Revision: https://dagster.phacility.com/D7433