message: Remove release-explorer.
  It does not appear to be used or maintained.
diff: @@ -72,10 +72,6 @@ It is generated by [rust-dxr](https://github.com/nrc/rust-dxr)
  It is split into a data [collector](https://github.com/rust-lang-nursery/rustc-perf/tree/master/collector) and a [web frontend](https://github.com/rust-lang-nursery/rustc-perf/tree/master/site). The raw performance data is available [here](https://github.com/rust-lang-nursery/rustc-timing) and can be browsed on the [perf website](https://perf.rust-lang.org).
  -## rust release explorer
  -
  -[rust release explorer](https://github.com/ashleygwilliams/rust-release-explorer/) is a way to explore rust release features based on milestone labels. The website can be found [here](https://ashleygwilliams.github.io/rust-release-explorer).
  -
  ## Rust Playground
  [Rust Playground](https://github.com/integer32llc/rust-playground) allows you to experiment with Rust before you install it locally, or in any other case where you might not have the compiler available. The Rust playground can be accessed [here](https://play.rust-lang.org).
  