Drop solver_competitions table

[jmg-duarte]

Description

Drop the solver_competitions table, which was kept only to provide frontend with solver-ids since cowprotocol/cowswap#7871 this is no longer the case and since #4657 this has been made effective turning this table obsolete

Changes

• Drop the solver_competitions table

[github-actions]

Reminder: Please update the DB Readme and comment whether migrations are reversible (include rollback scripts if applicable).

• If creating new tables, update the tables list.
• When adding a new index, consider using CREATE INDEX CONCURRENTLY for tables involved in the critical execution path.
• For breaking changes, remember that during rollout k8s starts the new autopilot, runs the Flyway migration, and only then shuts down the old pod. That overlap means the previous version can still be processing requests on the migrated schema, so make it compatible first and ship the breaking DB change in the following release.

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Caused by:

• database/sql/V115__drop_solver_competitions.sql

[claude]

Claude finished @jmg-duarte's task in 1m 28s —— View job

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PR Review: Drop solver_competitions table

• Read changed migration file
• Checked for remaining code references to solver_competitions
• Verified migration reversibility / rollout safety
• Posted review

The migration itself is correct and the change is safe:

• ✅ No live code references — grepped the whole workspace; only solver_competition_v2 (a different table) is used in Rust. The old solver_competitions module was already removed (per Remove dependency on the solver_competitions table #4657), so no deployed pod reads/writes this table during the rollout overlap.
• ✅ Not in the truncate lists in crates/database/src/lib.rs, so no update needed there.
• ✅ V115 is the latest migration — no numbering conflict.

One follow-up (posted inline): database/README.md still documents the ### solver_competitions section (lines 460–470). It should be removed so the schema docs stay in sync.

Note on reversibility: DROP TABLE is not reversible — dropped data is unrecoverable. That's clearly intentional here given the table is obsolete, but worth stating explicitly in the PR for the rollback checklist.

[MartinquaXD]

should also be dropped from the db readme as flagged by claude