Remove "builtins = _" from tox.ini
Remove "builtins = _" from tox.ini

"_" (ugettext_lazy) is defined by usual imports,
so "builtins = _" in tox.ini is unnecessary.

Change-Id: Idf90405b2af68fc120e1fe64e2f87484c60be493

openstack/senlin-dashboard,openstack/senlin-dashboard,stackforge/senlin-dashboard,stackforge/senlin-dashboard,openstack/senlin-dashboard,stackforge/senlin-dashboard,openstack/senlin-dashboard