python-axolotl: Disable tests for Python 2.x

The bump of setuptools from version 36.7.1 to 38.2.3 (commit
70c1899768) has caused the axolotl tests
to suddenly being run.

As the comment prior to the doCheck attribute states, we're using
pycryptodome so the tests are expected to fail even on Python 2.7 but
because of the version bump mentioned above, the tests didn't run and
thus the build didn't fail during when commit
094ac2d9b1 was made.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @abbradar, @Mic92

pkgs/top-level/python-packages.nix

@@ -6780,8 +6780,8 @@ in {
     };
 
     propagatedBuildInputs = with self; [ python-axolotl-curve25519 protobuf pycrypto ];
-    # IV == 0 in tests is not supported by pycrytpodom (our pycrypto drop-in)
-    doCheck = !isPy3k;
+    # IV == 0 in tests is not supported by pycryptodome (our pycrypto drop-in)
+    doCheck = false;
 
     meta = {
       homepage = "https://github.com/tgalal/python-axolotl";