gnu: python-pgpy: Update dependencies.

* gnu/packages/python-crypto.scm (python-pgpy)[native-inputs]: Move
python-cryptography, python-pyasn1, python-singledispatch, python-six from
here ...
[propagated-inputs]: ... to here.

gnu/packages/python-crypto.scm

@@ -1711,12 +1711,10 @@ signatures.")
              (when tests?
                (invoke "pytest")))))))
     (native-inputs
-     (list python-cryptography
-           python-pyasn1
-           python-pytest
-           python-singledispatch
-           python-six
+     (list python-pytest
            python-wheel))
+    (propagated-inputs (list python-cryptography python-pyasn1
+                             python-singledispatch python-six))
     (home-page "https://github.com/SecurityInnovation/PGPy")
     (synopsis "Python implementation of OpenPGP")
     (description