Cleanup Subscription#recently_renewed_with_multiple_amendments method

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### Problem

When using Amend API to perform a renewal operation, each type resulted in a separate amendment. For e.g. when upgrading a subscription, multiple amendments to Renew, Add product and Remove product will be generated. The latest version of the subscription may or may not be the Renewal amendment. Thus, when Zuora triggered a callback, the `amendment_types` attribute may or may not include `RenewSubscription`.

To circumvent this limitation, the method `Subscription#recently_renewed_with_multiple_amendments` was introduced to check if any of the amendments associated with the last transaction subscription included a `Renewal`.

The method is used when sending [online cloud notification](https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/ea526eded21642fd041170da5a53fe2f61f6425e/app/services/online_cloud_license_notification_service.rb#L14) email. Now that all renewals occur using Orders API, the first condition `renewal_amendment` should return `true` when the transaction included a Rewewal- as [`amendment_types` callback attribute](https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/ea526eded21642fd041170da5a53fe2f61f6425e/app/workers/zuora_callout/order_processed_worker.rb#L47) includes all [order action types translated into respective amendment types](https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/ea526eded21642fd041170da5a53fe2f61f6425e/app/workers/zuora_callout/order_processed_worker.rb#L41).

Consequently, the `Subscription#recently_renewed_with_multiple_amendments` method should be ready to cleanup.

### Proposal

<!-- Consult with `@gitlab-com/business-technology/enterprise-apps/zuora-architects` on the ~"Enterprise Applications" team if Zuora business logic is involved. -->

Before dropping the method, confirm the method is no longer being used:

- [x] Add a logger in the [`recently_renewed_with_multiple_amendments?` method](https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/ea526eded21642fd041170da5a53fe2f61f6425e/app/models/subscription.rb#L618) to ensure the code path does not reach the point when `base_subscription_id` is returned. This will confirm Amend API is not used for any of the existing workflows where the cloud notification is sent
- [x] Verify for all Renewal use cases `OnlineCloudLicenseNotificationService#execute` sends appropriate email (see https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/5944#note_1313873775)

- [x] Once above two verification is complete, the method can be dropped (and inclusion of logger module).

### Result

Cleanup of unused code.

### Next steps (if any)

### How will we measure success?

Story points: 2.0