Fix the legacy contract downloader and improve options related to it

[moonysolari]

• The legacyContractDownloader and officialAuthentication options toggle the same thing according to their descriptions. So, the latter is removed and the former is used in its stead.
• Fixed the legacy contract downloader for h3 by fixing the URL.
• Redid the logics regarding the contract downloaders such that
  • H1 and H2 will always use the legacy contract downloader, regardless of the value of legacyContractDownloader, because this is the only downloader they can use.
  • H3 will use the legacy contract downloader if legacyContractDownloader === true, and the HITMAPS downloader otherwise.
  • scpc will not use any downloader.
• Added a caveat for userAuths because it will only be non-empty if the legacy contract downloader is used.
• Removed redundant checks for location IDs because they no longer exist after Update H2LocationsData.json #92.

[AnthonyFuller]

LGTM.

[RDIL]

I am against this change. I can't remember the exact reason why, but it'll come back to me.