Remove prerequisites from deprecated Practice Exercises

[ee7]

From the spec:

• The "exercises.practice[].prerequisites" value must be an empty
  array if "exercises.practice[].status" is equal to deprecated

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This PR resolves an otherwise-upcoming CI failure - configlet lint will enforce this rule in the future.

The mensch-aergere-dich-nicht concept exercise is also deprecated, but already had an empty prerequisites array.

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[angelikatyborska]

Alrighty! But "practices" doesn't need to be empty?

[ee7]

But "practices" doesn't need to be empty?

It does. I just forgot it somehow, even though it's right there in the upcoming configlet lint output (see exercism/configlet#415 for context).

I've created #890 to make these practices arrays empty.