Use arb routines for fmpz_poly evaluation

[videlec]

Recent arb releases include functions to evaluate fmpz_poly at real ball arb_t (arb_fmpz_poly_evaluate_arb). We should replace fmpz_poly_evaluate_arb by it.

[saraedum]

This method has been introduced in arb 2.11.0 released on Jul 9, 2017.