Figure out if and why we should install chardet

[consideRatio]

I think we need to get to the bottom of if and why we should install chardet explicitly, and if so, what version we should constrain it to. Below are some reasons.

• https://github.com/jupyterhub/the-littlest-jupyterhub/blob/c6c6e34886a7d8be22ad8937f883899a89eea0fe/tljh/installer.py#L131-L145
• #708 - A failure related to chardet==3.0.4
• #642 - A failure related to chardet version 4, and a comment about its pinning: https://github.com/jupyterhub/the-littlest-jupyterhub/pull/719#discussion_r732783566
• traefik-proxy unpinned aiohttp, which requires chardet of a certain version: https://github.com/jupyterhub/traefik-proxy/pull/115/files#diff-4d7c51b1efe9043e44439a949dfd92e5827321b34082903477fd04876edb7552
• From https://github.com/2i2c-org/upstream/issues/17 I read:

  jupyterhub-traefik-proxyhas aiohttp pinned to an older version so that it works with the consul python client. However, this pin clashed with chardet latest version and impacted tljh-configfunctionality and has been fixed by pinning thechardetversion.

My guess, quite confused about things still, is that we could stop using a pin of chardet in tljh.