Branches page shows incorrect download artefacts button

The Projects::BranchesController loads @ref_pipelines and @branch_pipeline_statuses and then the frontend uses the @ref_pipelines to display the download artefacts button and @branch_pipeline_statues to show the ci status icon for each branch.

There are 2 issues here.

1. We're using 2 queries to fetch what should be the same pipeline.
2. These queries behave slightly differently and @ref_pipelines is actually not as reliable

We should remove @ref_pipelines and update the download artefacts logic.