Update Elixir documentation (1.16 and 1.17)

[breunigs]

The guides have moved from a separate page into the same documentation system. This required shuffling of the cleanup functions, which is subtly incompatible with the docs of the older versions, or would have required if/else in various places. For legibility, I thus opted to remove old versions.

If you're updating existing documentation to its latest version, please ensure that you have:

• Updated the versions and releases in the scraper file
• Ensured the license is up-to-date
• Ensured the icons and the SOURCE file in public/icons/your_scraper_name/ are up-to-date if the documentation has a custom icon
• Ensured self.links contains up-to-date urls if self.links is defined
• Tested the changes locally to ensure:
  • The scraper still works without errors
  • The scraped documentation still looks consistent with the rest of DevDocs
  • The categorization of entries is still good

[simon04]

Thank you!