Remove inner private class JacobiPolynomials.JacobiKey
Since JacobiKey is now a public class in Hipparchus (see Hipparchus issue 322), there's no need to have it duplicated in Orekit class JacobiPolynomials
Since JacobiKey is now a public class in Hipparchus (see Hipparchus issue 322), there's no need to have it duplicated in Orekit class JacobiPolynomials