Revert "[AIRFLOW-6929] Add OpenAPI spec (#7549)"

[ashb]

This reverts commit 11f1e0c.

The OpenAPI spec as added in has problems and needs revisiting (typos,
wrong IDs, wrong types). Sorry to do this, but

1. PR Add OpenAPI spec #7549 never had any approval, and the AIP never linked to that PR. (1b. AIP vote passing does not equal PR approval. Every PR still needs approval. AIP vote is not code review.)
2. It has the mistakes that you said you fixed in the AIP were not fixed.
3. There are open questions around the IDs we use.
4. All the typos that were left as a comment on the polidea PR before you merged this PR.

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[ashb]

See also the mailing list post I'm about to start about the id types for connection and Dag Run.

[potiuk]

Agree. The PR had no approvals it is NotCool indeed.