Remove tox locale overrides

* tox.ini: The LANG, LANGUAGE and LC_ALL environment overrides were
introduced originally during the testr migration in an attempt to be
conservative about the possibility that locale settings in the
calling environment could cause consistency problems for test runs.
In actuality, this should be unnecessary and any place where it does
cause issues ought to be considered an actual bug. Also, having
these in the configuration actively causes older pip to have
problems with non-ASCII content in some package metadata files under
Python 3, so drop it now.

Change-Id: If4e025e22248d06b77e9d4d8f4e4815776428b9d
Closes-Bug: #1277495

tox.ini

@@ -7,9 +7,6 @@ skipsdist = True
 usedevelop = True
 install_command = pip install -U {opts} {packages}
 setenv = VIRTUAL_ENV={envdir}
-         LANG=en_US.UTF-8
-         LANGUAGE=en_US:en
-         LC_ALL=C
 
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt