Google says it has retired the feature-phone user agents for crawling content for feature-phones. No surprise there. Although there are probably a lot of feature phones around, I wonder how many people actually use search with a feature-phone.
If you provide content for feature-phones via dynamic serving you should use a self-referential alternate URL link for handheld (feature-phone) devices:
<link rel="alternate" media="handheld" href="[current page URL]" />
This is a change from previous documentation for feature-phones of only using the "vary: user-agent" HTTP header.
Feature-phone tools are going to disappear from the search console.
Here's the link to making feature-phone content. [developers.google.com