docs: Remove empty frontend document

Author: Turbo87

docs/ARCHITECTURE.md

@@ -37,8 +37,7 @@ The backend stores information in a Postgres database.
 
 ## Frontend - Ember.js
 
-The frontend of crates.io is written in JavaScript using [Ember.js][]. More information about the
-frontend is in [`docs/FRONTEND.md`](https://github.com/rust-lang/crates.io/blob/master/docs/FRONTEND.md).
+The frontend of crates.io is written in JavaScript using [Ember.js][]. More information about frontend development is in [`docs/CONTRIBUTING.md`](https://github.com/rust-lang/crates.io/blob/master/docs/CONTRIBUTING.md).
 
 [Ember.js]: https://emberjs.com/