Backend: Follow-up from deprecation of DAG tab: remove associated code

Summary

From the discussion in #336560 (closed) and gl-retrospectives/verify-stage/pipeline-authoring#49 (comment 1916361556) recently, the removing of the Needs tab could provide a performance improvement and remove a bug at the same time for a tab that may not be useful

Proposal

Remove any backend code not needed anymore that supported the Needs tab display.

NOTE: This is going off the assumption that there is any backend code that needs to be removed. Some investigation may need to happen prior to this work being prioritized.

Confirm purpose and User Reception (how does this benefit the user?)

N/A

Additional details

Some relevant technical details, if applicable, such as:

• Does this need a feature flag?
• Does there need to be an associated instrumentation issue created related to this work?
• Is there an example response showing the data structure that should be returned (new endpoints only)?
• What permissions should be used?
• Is this EE or CE?
  • EE
  • CE
• Additional comments:

Links/References