remove pytidylib and netifaces from tox.ini external dependency

pytidylib is introduced on Jan 27, 2014 by
commit: 3257d83bbb,
changeId: I73f3202ac7a1420aaa303d5ea2e741b2fe5673e9
https://review.openstack.org/#/c/69491/

but actually not used, nor used by packages depended by us. The commit
message, review comments and bug report don't provide details for this
change.

netifaces is introduced Jan 21 2014 by:
commit: 28f6bee013
changeId: I1721804890423c242bb69697d2c42ca57d0871a4

At that time, it is required by swift, but now we have removed swift from
{test-}requirements.
Now it is only required by oslo.utils.netutils, but can be downloaded
via pypi, see:
https://github.com/openstack/oslo.utils/blob/1.2.0/requirements.txt#L11

Change-Id: I8bff587892396c32b327049b024e6e8acfff64cf
Closes-Bug: #1413455

tox.ini

@@ -6,7 +6,7 @@ envlist = py27,py33,py34,py-mysql,py-pgsql,pep8
 [testenv]
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
-install_command = pip install -U --allow-external pytidylib --allow-insecure pytidylib --allow-external netifaces --allow-insecure netifaces {opts} {packages}
+install_command = pip install -U {opts} {packages}
 usedevelop = True
 setenv = VIRTUAL_ENV={envdir}
          EVENTLET_NO_GREENDNS=yes