Remove `:dag_pipeline_tab` flag

Merged Sarah Groff Hennigh-Palermo requested to merge remove-dag-ff into master

What does this MR do?

The :dag_pipeline_tab has been on by default since %13.2, so I think we can remove it now.

Screenshots (strongly suggested)

Screen_Shot_2021-01-21_at_2.38.43_PM

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing