Remove requirements.txt from tox.ini deps

This is redundant, per lifeless email:
http://lists.openstack.org/pipermail/openstack-dev/2015-July/069663.html

Change-Id: Ie78d0e5b2fc8274867f2c6013b04ae9e0796f81f

tox.ini

@@ -9,8 +9,7 @@ install_command = pip install -U {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
          PYTHONDONTWRITEBYTECODE = 1
          LANGUAGE=en_US
-deps = -r{toxinidir}/requirements.txt
-       -r{toxinidir}/test-requirements.txt
+deps = -r{toxinidir}/test-requirements.txt
 whitelist_externals = bash
 commands =
   bash -c "TESTS_DIR=./ironic/tests/ python setup.py testr --slowest --testr-args='{posargs}'"