Remove get_readable_dag, get_editable_dag, and get_accessible_dags.

[jhtimmins]

As part of cleaning up FAB, we're minimizing the size of the interface by removing unnecessary helper methods. This PR removes get_readable_dags, get_editable_dags, and get_accessible_dags.

[bbovenzi]

UI still seems to work but I can't comment on the code itself.

[github-actions]

The PR is likely OK to be merged with just subset of tests for default Python and Database versions without running the full matrix of tests, because it does not modify the core of Airflow. If the committers decide that the full tests matrix is needed, they will add the label 'full tests needed'. Then you should rebase to the latest main or amend the last commit of the PR, and push it with --force-with-lease.

[ashb]

Why though?

It seems expensive to have to get full DAGModel objects just to then throw away all that info and keep the dag_ids only.

How many places do we actually use get_readable_dags etc and want the dags vs the IDs?

Would it perhaps make more sense to replace get_accessible_dags with a get_accesible_dag_ids that directly returns the IDs?

[jhtimmins]

@ashb good call. That was actually a simpler change overall, which I've made.