Fix error handling logic during license removal in ee/app/assets/javascripts/admin/subscriptions/show/components/subscription_breakdown.vue

From !199147 (merged):

[T]he implementation doesn't work as the tests expected, since an error instance is passed to createAlert, and not a string. This also means that two tests cannot pass in reality, since an error instance is always truthy, and it'll always be different error instances each time. So, those tests were removed.

We could fix the implementation here, but it's out of scope for fixing Vue 3 specs.

See the following thread/MR for context:

• @agulina started a discussion:

  Thanks for the comment.

  I noticed a bunch of changes here were introduced in the context of Use VueX store for admin subscription component (!104176 - merged).

  Should we create a follow-up to address this?