[Deprecation] created_by_description, created_by_title fields

## Planned Removal Date
October 1st, 2026

## Original Deprecation PR Link
[Shopify 162](https://github.com/fivetran/dbt_shopify/pull/162)

## Deprecated Item Type
- Field

## Deprecated Item
The following fields are slated to be removed from the [`stg_shopify__discount_redeem_code`](https://github.com/fivetran/dbt_shopify/blob/main/models/rest/staging/stg_shopify__discount_redeem_code.sql) and [`stg_shopify_gql__discount_redeem_code`](https://github.com/fivetran/dbt_shopify/blob/main/models/graphql/staging/stg_shopify_gql__discount_redeem_code.sql) models:
- `created_by_description`
- `created_by_title`

## Rationale and Impact Analysis
These fields are being removed due to not being referenced in any downstream models.

Read the linked original deprecation PR, then inspect models/rest/staging/stg_shopify__discount_redeem_code.sql and models/graphql/staging/stg_shopify_gql__discount_redeem_code.sql. Confirm both deprecated fields are removed from the staging models and that no downstream references remain.

Written by the indexing model from the issue text.