ci: remove orahub .gitlab-ci.yml — root cause of failure noise

[fede-kamel]

Mirrors orahub MR !105 (root-cause fix for the docs pipeline failures).

Diagnosis

• Project shared_runners_enabled: False on orahub (flipped to True via API, no effect — no instance runners visible).
• 0 project runners, 0 group runners.
• Every pipeline sat in the queue 1–4h with started_at: null and timed out as failed.
• The pages job on main has been failing since the file was added — docs were never published via orahub.

Real publishing path

.github/workflows/docs.yml builds + publishes to GitHub Pages on every push to main. That's the canonical URL.

Fix

Delete .gitlab-ci.yml. No pipeline = no notification. The earlier allow_failure: true change (#20) was a symptom suppressant; this is the cause.