Inform that billing is empty in removal notifications

[orangesunny]

Describe the problem

A user gets scared when they receive a notification about expiring/terminated/removed billing. In some cases, there’s no project name, probably because such billing is an empty one previously used for testing.

Describe the solution you'd like

• Use the sentence
  No projects in this billing. You might have other billings with projects in.
  where projects are listed if the billing has some.

• remove following from removal notification e-mail:
  Your trial period is going to expire in less than a week. If you like Weblate and you want to continue using it, just request an approval of your libre plan.

Describe alternatives you've considered

No response

Screenshots

this is how it currently looks in the e-mail

Additional context

https://care.weblate.org/#ticket/zoom/6219

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