FIX: Remove old seeded prompts. (#17)

We switched to negative integers for seeded prompts, but we also
need to delete the old ones using IDs 1/2/3 if they exist,
 or deploys will fail due to the unique index on the name column.

db/migrate/20230320122645_delete_duplicated_seeded_prompts.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+class DeleteDuplicatedSeededPrompts < ActiveRecord::Migration[7.0]
+  def up
+    DB.exec <<~SQL
+      DELETE FROM completion_prompts
+      WHERE (
+        (id = 1 AND name = 'translate') OR
+        (id = 2 AND name = 'generate_titles') OR
+        (id = 3 AND name = 'proofread')
+      )
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end