Remove dependency on pytest-elasticsearch.

tox.ini

@@ -5,7 +5,6 @@ envlist=flake8,py3
 deps =
   .[testing]
   pytest-cov
-  https://github.com/ClearcodeHQ/pytest-elasticsearch/tarball/master#egg=pytest-elasticsearch
 commands =
   pytest --cov={envsitepackagesdir}/swh/search \
          {envsitepackagesdir}/swh/search \