The twitter gem had several problems:
* It's been unmaintained for over a year.
* It pulled in a lot of dependencies, many of which were outdated. In
particular, it locked the `http` gem to version 3.3, preventing us
from upgrading to 4.2.
* It raised exceptions on normal error conditions, like for deleted
tweets or suspended users, which we really don't want.
* We had to wrap it to provide caching.
Changes:
* Fixes#4226 (Exception when creating new artists entries for suspended
Twitter accounts)
* Drop support for scraping images from summary cards. Summary cards
are the previews you get when you link to a website in a tweet. These
preview images aren't always the best image.
