Doc/impl inconsistency for MPolynomial_libsingular.reduce()

[mezzarobba]

The docstring of sage.rings.polynomial.multi_polynomial_libsingular.MPolynomial_libsingular.reduce() says:

        INPUT: 

        - ``I`` - a list/set of polynomials. If ``I`` is an ideal, the
          generators are used.

However:

sage: R.<x,y> = QQ[]
sage: J = R.ideal(x^2 + y^2 - 1, 16*x^2*y^2 - 1)
sage: (y^4).reduce(J.gens())
y^4
sage: (y^4).reduce(J)
y^2 - 1/16

Component: commutative algebra

Issue created by migration from https://trac.sagemath.org/ticket/11671