V184: removes the shop_currency setting seeded by V135.

Nothing reads it — confirmed by a full grep over phoenix_kit, phoenix_kit_billing, phoenix_kit_ecommerce, and a host application: the only occurrences of the key are the V135 seed itself and this package's ExpectedSchema manifest that audits V135's shape. The default currency a shop actually uses is the is_default = true row of phoenix_kit_currencies, resolved through PhoenixKitBilling.get_default_currency/0 — and nothing else. A second, identically-named "shop currency" that does nothing is exactly the kind of trap the next reader falls into, assuming it is the thing that's read.

Why V135 itself is not edited

The seed is INSERT ... ON CONFLICT ("key") DO NOTHING. Every host that has already migrated already has the row — deleting the line from V135's text changes nothing for them, since a past migration's execute/1 calls do not re-run. It would only change behavior for a brand-new install, which is exactly the population that has no problem to fix. Worse, V135 is a released, hashed baseline: editing it changes ExpectedSchema.chain_hash/0 and fails mix phoenix_kit.release_check for every host already on this version, for a change that helps nobody. The correct place for a removal is a new chain version, which is what this migration is.

down/1

Restores the row with the exact statement V135 seeded it with (copied verbatim, including the ON CONFLICT ("key") DO NOTHING), so a rollback never overwrites a value an operator may have re-created by hand after the key was deleted — it only recreates the row if one is not already there.