Drop enabled_foundational_flow_check_results table

What does this MR do and why?

This drops enabled_foundational_flow_check_results table which was never used in production and has no data. The reasoning behind the drop was explained in !257212 (merged) and this MR finalizes the deletion by dropping the table.

Database review notes

• The table is empty and no application code writes to it.
• Both foreign key targets, enabled_foundational_flows and organizations, are small or medium tables and foreign key removals use with_lock_retries.
• The migrations are idempotent: they use if_exists and remove_foreign_key_if_exists.

References

• Issue: #628248 (closed)
• Step 1 MR: !257212 (merged)

Screenshots or screen recordings

Not applicable. This change only touches the database.

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