exercises/concept/*: rm unnecessary allow(unused)

Author: petertseng

exercises/concept/assembly-line/src/lib.rs

@@ -1,7 +1,3 @@
-// This stub file contains items that aren't used yet; feel free to remove this module attribute
-// to enable stricter warnings.
-#![allow(unused)]
-
 pub fn production_rate_per_hour(speed: u8) -> f64 {
     unimplemented!("calculate hourly production rate at speed: {}", speed)
 }

exercises/concept/lucians-luscious-lasagna/src/lib.rs

@@ -1,7 +1,3 @@
-// This stub file contains items that aren't used yet; feel free to remove this module attribute
-// to enable stricter warnings.
-#![allow(unused)]
-
 pub fn expected_minutes_in_oven() -> i32 {
     unimplemented!("return expected minutes in the oven")
 }

exercises/concept/role-playing-game/src/lib.rs

@@ -1,7 +1,3 @@
-// This stub file contains items that aren't used yet; feel free to remove this module attribute
-// to enable stricter warnings.
-#![allow(unused)]
-
 pub struct Player {
     pub health: u32,
     pub mana: Option<u32>,