[autotest] external_packages: remove dnspython

The last remaining user of this module seems to have been removed in
https://chromium-review.googlesource.com/203106

BUG=None
TEST=None

Change-Id: If9e6935f557a14b417b5d5137dcdd057c4d735d8
Reviewed-on: https://chromium-review.googlesource.com/403215
Commit-Ready: Aviv Keshet <akeshet@chromium.org>
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Dan Shi <dshi@google.com>
diff --git a/utils/external_packages.py b/utils/external_packages.py
index f8f559e..ecae0c1 100644
--- a/utils/external_packages.py
+++ b/utils/external_packages.py
@@ -817,35 +817,6 @@
         return self.version
 
 
-class DnsPythonPackage(ExternalPackage):
-    """
-    dns module
-
-    Used in unittests.
-    """
-    module_name = 'dns'
-    version = '1.3.5'
-    url_filename = 'dnspython-%s.tar.gz' % version
-    local_filename = url_filename
-    urls = ('http://www.dnspython.org/kits/%s/%s' % (
-        version, url_filename),)
-
-    hex_sum = '06314dad339549613435470c6add992910e26e5d'
-
-    _build_and_install = ExternalPackage._build_and_install_from_package
-    _build_and_install_current_dir = (
-                        ExternalPackage._build_and_install_current_dir_noegg)
-
-    def _get_installed_version_from_module(self, module):
-        """Ask our module its version string and return it or '' if unknown."""
-        try:
-            __import__(self.module_name + '.version')
-            return module.version.version
-        except AttributeError:
-            logging.error('could not get version from %s', module)
-            return ''
-
-
 class PyudevPackage(ExternalPackage):
     """
     pyudev module