python3-cryptography: remove test_x509.py

We already have removed --benchmark-disable option to avoid
adding python3-pytest-benchmark rdepends.

Also remove the case test_x509.py which needs benchmark feature
to avoid below failure:
 file /usr/lib64/python3-cryptography/ptest/tests/bench/test_x509.py, line 9
  def test_aki_public_bytes(benchmark):
 >       fixture 'benchmark' not found
 >       available fixtures: backend, cache, capfd, capfdbinary, caplog, capsys, capsysbinary, disable_rsa_checks, doctesty
 >       use 'pytest --fixtures [testpath]' for help on them.

Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>