ci: remove orphaned API reference workflow

[localhost41]

What changed

Removed the scheduled API-reference workflow. The generator it invokes was intentionally removed in #179, but the workflow remained in the repository and has continued to run from the default branch every six hours. Each run now fails immediately because scripts/api-ref-gen no longer exists.

This keeps the decision from #179 intact while stopping the recurring failed runs.

Verification

• Confirmed scripts/api-ref-gen is absent from develop
• Confirmed recent workflow runs fail at the missing generator working directory
• git diff --check

[localhost41]

Refreshed this onto current develop. The orphaned schedule is still firing every six hours; the latest run (32083327034) failed immediately because the scripts/api-ref-gen working directory no longer exists. This remains a single deletion of the stale workflow; git diff --check and the 20 generator-independent tests pass. Could someone take a look when convenient?