fix: remove repl.it support for now

It stopped working and needs too much manual fixing, until someone
comes along to fix it, it's not great to have in the README section.

Closes #1352.

Author: manyinsects

.replit

@@ -62,8 +62,6 @@ If you get a permission denied message, you might have to exclude the directory
 
 ## Browser
 
-[Run on Repl.it](https://repl.it/github/rust-lang/rustlings)
-
 [![Open in Gitpod](https://gitpod.io/button/open-in-gitpod.svg)](https://gitpod.io/#https://github.com/rust-lang/rustlings)
 
 [![Open Rustlings On Codespaces](https://github.com/codespaces/badge.svg)](https://github.com/codespaces/new/?repo=rust-lang%2Frustlings&ref=main)