Follow-up from "Add GET /licenses and DELETE /license/:id API"

The following discussions from !9733 (merged) should be addressed:

@jeremy started a discussion: (+2 comments)

Can we consider an approach described in https://gitlab.com/gitlab-org/gitlab-ee/issues/8292? I don't know if hard-coding 1.year will always be the right option. cc @rdavila

What do you think about using a context to make it clear that the current user is an admin?
context 'when the current user is an admin' do
  let(:current_user) { create(:admin) }

  it { is_expected.to be_allowed(:read_licenses) }
  it { is_expected.to be_allowed(:destroy_licenses) }
end
Not exactly important, let's do it later.

@godfat started a discussion:

We don't exactly have a test to make sure that the numbers should be correct here, but I think the code looks correct and we can add the tests later anyway. At worst the number can be wrong, which I assume it won't be too harmful :P