Remove Six dependency

[hacklschorsch]

We used ​Six to migrate from Python 2 to 3; now that we're all Python 3, we would like to live without it.

[meejah]

I still see a bunch of "six" imports, from a quick grep:

$ git grep "six import" 
integration/test_streaming_logs.py:from six import ensure_text
src/allmydata/client.py:from six import ensure_text
src/allmydata/immutable/downloader/finder.py:from six import ensure_str
src/allmydata/immutable/upload.py:from six import ensure_str
src/allmydata/introducer/client.py:from six import ensure_text, ensure_str
src/allmydata/introducer/server.py:from six import ensure_text
src/allmydata/mutable/checker.py:from six import ensure_str
src/allmydata/mutable/servermap.py:from six import ensure_str
src/allmydata/node.py:from six import ensure_str, ensure_text
src/allmydata/scripts/admin.py:from six import ensure_binary
src/allmydata/scripts/slow_operation.py:from six import ensure_str
src/allmydata/scripts/tahoe_check.py:from six import ensure_text
src/allmydata/scripts/tahoe_ls.py:from six import ensure_text
src/allmydata/test/cli/common.py:from six import ensure_str, ensure_text
src/allmydata/test/cli/test_check.py:from six import ensure_text
src/allmydata/test/cli/test_cli.py:from six import ensure_text
src/allmydata/test/cli/test_status.py:from six import ensure_text
src/allmydata/test/common_web.py:from six import ensure_str
src/allmydata/test/eliotutil.py:from six import ensure_text
src/allmydata/test/no_network.py:from six import ensure_text
src/allmydata/test/storage_plugin.py:from six import ensure_str
src/allmydata/test/test_deepcheck.py:from six import ensure_text
src/allmydata/test/test_introducer.py:from six import ensure_binary, ensure_text
src/allmydata/test/test_multi_introducers.py:from six import ensure_binary
src/allmydata/test/test_storage.py:from six import ensure_str
src/allmydata/test/test_system.py:from six import ensure_text
src/allmydata/test/web/test_web.py:from six import ensure_binary
src/allmydata/util/eliotutil.py:from six import ensure_text
src/allmydata/util/encodingutil.py:from six import ensure_str
src/allmydata/util/idlib.py:from six import ensure_text
src/allmydata/util/log.py:from six import ensure_str
src/allmydata/web/common.py:from six import ensure_str
src/allmydata/webish.py:from six import ensure_str

[hacklschorsch]

Thanks @meejah, you were right - Six is still in use, I was wrong. I updated the description of the ticket - I think the title is still apt?

Removing six is WIP, for example in ​https://github.com/tahoe-lafs/tahoe-lafs/pull/1423 .