src/sage/rings/power_series_ring.py: Fix import

Author: Matthias Koeppe

src/sage/rings/power_series_ring.py

@@ -152,7 +152,6 @@
 from sage.rings.polynomial.multi_polynomial_ring_base import is_MPolynomialRing
 from sage.rings.polynomial.polynomial_ring import is_PolynomialRing
 from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
-from sage.rings.power_series_pari import PowerSeries_pari
 from sage.structure.category_object import normalize_names
 from sage.structure.element import Expression, parent
 from sage.structure.nonexact import Nonexact