Simplify modular inversion fuzzer
Simplify modular inversion fuzzer

Now binary ext gcd algorithm has an exposed API so no need to
duplicate the code here.

webmaster128/botan,randombit/botan,webmaster128/botan,randombit/botan,webmaster128/botan,randombit/botan,webmaster128/botan,randombit/botan,webmaster128/botan,randombit/botan