Remove all six functionality

[dorothykiz1]

six provides simple utilities for wrapping over differences between Python 2 and Python 3.

Follow this guide https://six.readthedocs.io/to find python 3 equivalent for python 2 six functionality.

Remove all six imports and functionality and replace them with python 3 equivalent.
ie. from six.xrange() to range()

[Leenkiz]

#take

[datapythonista]

Those are all the uses of six that we still got pending:

asv/step_detect.py:import six
asv/graph.py:from six.moves import xrange
asv/util.py:import six
asv/util.py:from six.moves import xrange
asv/plugins/regressions.py:from six.moves.urllib.parse import urlencode
asv/commands/preview.py:from six.moves import SimpleHTTPServer, socketserver
asv/commands/quickstart.py:from six.moves import input as raw_input
asv/results.py:from six.moves import zip as izip
test/test_workflow.py:import six
test/test_console.py:import six
test/tools.py:import six
test/tools.py:from six.moves import SimpleHTTPServer
test/test_web.py:from six.moves.urllib.parse import parse_qs, splitquery, splittag
test/test_results.py:import six