TYP: fix stubtest errors in numpy.lib._arraysetops_impl

Ported from numpy/numtype#234

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This fixes the signatures of the following public `numpy` members:

- `unique`
- `unique_all`
- `unique_counts`
- `unique_inverse`
- `unique_values`
- `intersect1d`
- `ediff1d`

Author: jorenham