Revert "Start backend with rocket.rs"

This reverts commit 28011b8f93.

rs/src/main.rs

@@ -1,20 +0,0 @@
-#[macro_use]
-extern crate rocket;
-use rocket::serde::{json::Json, Serialize};
-
-#[derive(Serialize)]
-struct Greeting<'a> {
-    hello: &'a str,
-}
-
-#[get("/")]
-fn index() -> Json<Greeting<'static>> {
-    Json(Greeting {
-        hello: "Hello, world!",
-    })
-}
-
-#[launch]
-fn rocket() -> _ {
-    rocket::build().mount("/api/", routes![index])
-}