Cleanup new_without_default workarounds

bin/ensure_stubs_compile.sh

@@ -61,7 +61,7 @@ for dir in $changed_exercises; do
         # since we're generally not going to test it.
         if ! (
             cd "$dir" &&
-            cargo clippy --lib --tests --color always -- --allow clippy::new_without_default 2>clippy.log
+            cargo clippy --lib --tests --color always -- 2>clippy.log
         ); then
             cat "$dir/clippy.log"
             broken="$broken\n$exercise"

exercises/practice/grade-school/src/lib.rs

@@ -1,10 +1,3 @@
-// This annotation prevents Clippy from warning us that `School` has a
-// `fn new()` with no arguments, but doesn't implement the `Default` trait.
-//
-// Normally, it's good practice to just do what Clippy tells you, but in this
-// case, we want to keep things relatively simple. The `Default` trait is not the point
-// of this exercise.
-#[allow(clippy::new_without_default)]
 pub struct School {}
 
 impl School {