Upstream nixpkgs has upgraded these packages

So we don't have to override them to get a new version anymore.  Also,
upstream has done a better job of integrating them into the overall system
than we have (with respect to other upstream changes).

autobahn.nix

-{ lib, buildPythonPackage, fetchFromGitHub, isPy3k,
-  six, txaio, twisted, zope_interface, cffi, trollius, futures, cryptography,
-  mock, pytest,
-  supportAsyncio ? false
-}:
-buildPythonPackage rec {
-  pname = "autobahn";
-  version = "19.7.1";
-
-  src = fetchFromGitHub {
-    owner = "crossbario";
-    repo = "autobahn-python";
-    rev = "v${version}";
-    sha256 = "1gl2m18s77hlpiglh44plv3k6b965n66ylnxbzgvzcdl9jf3l3q3";
-  };
-
-  propagatedBuildInputs = [ six txaio twisted zope_interface cffi cryptography ] ++
-    (lib.optionals (!isPy3k) [ futures ]) ++
-    (lib.optionals (supportAsyncio && !isPy3k) [ trollius ])
-    ;
-
-  checkInputs = [ mock pytest ];
-  checkPhase = ''
-    runHook preCheck
-    USE_TWISTED=true py.test $out
-    runHook postCheck
-  '';
-
-  # XXX Fails for some reason I don't understand.
-  doCheck = false;
-
-  meta = with lib; {
-    description = "WebSocket and WAMP in Python for Twisted and asyncio.";
-    homepage    = "https://crossbar.io/autobahn";
-    license     = licenses.mit;
-    maintainers = with maintainers; [ nand0p ];
-  };
-}

cryptography.nix

-{ stdenv
-, buildPythonPackage
-, fetchFromGitHub
-, openssl
-, cryptography_vectors
-, darwin
-, asn1crypto
-, packaging
-, six
-, pythonOlder
-, enum34
-, ipaddress
-, isPyPy
-, cffi
-, pytest
-, pretend
-, iso8601
-, pytz
-, hypothesis
-}:
-
-buildPythonPackage rec {
-  pname = "cryptography";
-  version = "2.7"; # Also update the hash in vectors.nix
-
-  src = fetchFromGitHub {
-    owner = "pyca";
-    repo = "cryptography";
-    rev = "2.7";
-    sha256 = "145byri5c3b8m6dbhwb6yxrv9jrr652l3z1w16mz205z8dz38qja";
-  };
-
-  outputs = [ "out" "dev" ];
-
-  buildInputs = [ openssl ]
-             ++ stdenv.lib.optional stdenv.isDarwin darwin.apple_sdk.frameworks.Security;
-  propagatedBuildInputs = [
-    asn1crypto
-    packaging
-    six
-  ] ++ stdenv.lib.optional (pythonOlder "3.4") enum34
-  ++ stdenv.lib.optional (pythonOlder "3.3") ipaddress
-  ++ stdenv.lib.optional (!isPyPy) cffi;
-
-  checkInputs = [
-    cryptography_vectors
-    hypothesis
-    iso8601
-    pretend
-    pytest
-    pytz
-  ];
-
-  checkPhase = ''
-    py.test --disable-pytest-warnings tests
-  '';
-
-  # IOKit's dependencies are inconsistent between OSX versions, so this is the best we
-  # can do until nix 1.11's release
-  __impureHostDeps = [ "/usr/lib" ];
-
-  meta = with stdenv.lib; {
-    description = "A package which provides cryptographic recipes and primitives";
-    longDescription = ''
-      Cryptography includes both high level recipes and low level interfaces to
-      common cryptographic algorithms such as symmetric ciphers, message
-      digests, and key derivation functions.
-      Our goal is for it to be your "cryptographic standard library". It
-      supports Python 2.7, Python 3.4+, and PyPy 5.3+.
-    '';
-    homepage = https://github.com/pyca/cryptography;
-    license = with licenses; [ asl20 bsd3 psfl ];
-    maintainers = with maintainers; [ primeos ];
-  };
-}

cryptography_vectors.nix

-{ buildPythonPackage, fetchPypi, lib, cryptography }:
-
-buildPythonPackage rec {
-  pname = "cryptography_vectors";
-  # The test vectors must have the same version as the cryptography package:
-  version = cryptography.version;
-
-  src = fetchPypi {
-    inherit pname version;
-    sha256 = "1g38zw90510azyfrj6mxbslx2gp9yrnv5dac0w2819k9ssdznbgi";
-  };
-
-  # No tests included
-  doCheck = false;
-
-  meta = with lib; {
-    description = "Test vectors for the cryptography package";
-    homepage = https://cryptography.io/en/latest/development/test-vectors/;
-    # Source: https://github.com/pyca/cryptography/tree/master/vectors;
-    license = with licenses; [ asl20 bsd3 ];
-    maintainers = with maintainers; [ primeos ];
-  };
-}

overlays.nix

@@ -17,13 +17,6 @@ self: super: {
 
       # new tahoe-lafs dependency
       eliot = python-super.callPackage ./eliot.nix { };
-      # new autobahn requires a newer cryptography
-      cryptography = python-super.callPackage ./cryptography.nix { };
-      # new cryptography requires a newer cryptography_vectors
-      cryptography_vectors = python-super.callPackage ./cryptography_vectors.nix { };
-      # new tahoe-lafs depends on a very recent autobahn for better
-      # websocket testing features.
-      autobahn = python-super.callPackage ./autobahn.nix { };
 
       # tahoe-lafs in nixpkgs is packaged as an application!  so we have to
       # re-package it ourselves as a library.