Remove EnabledFoundationalFlowCheckResult model

What does this MR do and why?

EnabledFoundationalFlowCheckResult was introduced on GitLab 18.11 and no code writes to it yet. The table structure does not fit what we need anymore and that work was deprioritized, so fixing the sharding key now is not worth the time and I decided to remove the table instead.

This MR removes the model and every reference to it. No code reads or writes this model today and the table is empty, so this change has no effect on behavior.

The table itself stays for now. A follow-up MR will drop it.

References

• Issue: #628248 (closed)
• Follow-up MR: !257213 (merged)

Screenshots or screen recordings

Not applicable. This change removes unused code. It does not change the UI.

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