Prune inherited upstream branches from dataform-co/dataform

[ihistand]

Follow-up to #12. origin carries 102 branches inherited from dataform-co/dataform when this repo was created — old upstream PR/feature branches that have nothing to do with SQLAnvil (add-assertion-option, bq-cost, bump_bigquery_client_*, cached_builds, apilaskowski-patch-1, …). They're pure noise in the branch list.

Scope

• Delete the ~102 inherited upstream branches on origin.
• Keep main and dataform (the upstream reference snapshot).
• These came from upstream, not from SQLAnvil work, so none should have SQLAnvil PRs or unmerged SQLAnvil content.

Approach (proposed)

• The full, current upstream history is always re-fetchable from the upstream remote (dataform-co/dataform), so deleting these copies on origin loses nothing.
• Batch-delete via git push origin --delete <names...> (scripted from git branch -r, filtered to exclude main/dataform).
• Spot-check a sample first to confirm none were repurposed for SQLAnvil work (none expected).

Caution

• Large batch delete against the shared remote — double-check the keep-list (main, dataform) before running.
• Confirm there are no open PRs backed by any of these branches (after Prune stale merged branches (SQLAnvil reintegration/rename work) #12 there should be 0 open PRs).