Don't require checking that an exercise runs

Author: mo8it

CONTRIBUTING.md

@@ -41,7 +41,6 @@ When updating an exercise, check if its solution needs to be updated.
 - In the exercise, add a `// TODO: …` comment where user changes are required.
 - Add a solution at `solutions/yourTopic/yourTopicN.rs` with comments explaining it.
 - Add the [metadata for your exercise](#exercise-metadata) in the `rustlings-macros/info.toml` file.
-- Make sure your exercise runs with `rustlings run yourTopicN`.
 - [Open a pull request](#pull-requests).
 
 ### Exercise Metadata