Remove redundant request for fetching billable members

What does this MR do?

Attempting to resolve the problem with the help popover turned into a small refactor to improve the performance of our billing page a bit.

To initialize the subscriptions table we make two requests to get:

1. The subscription information.
2. The first page of billable members to show the button See usage.

But the 2nd request is redundant because we show this button regardless of the count of billable members. We show it for groups and we can pass that information right from the backend when we instantiate our application. And by doing that we are no longer required to send this request hence we can remove it safely.

Closes #320905 (closed).

Screenshots (strongly suggested)

Nothing changed visually.

Does this MR meet the acceptance criteria?

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