Remove unnecessary scopes in App methods (#7813)

# Objective

A couple of places in `bevy_app` use a scoped block that doesn't do anything. I imagine these are a relic from when `Mut<T>` implemented `Drop` in the early days of bevy.

## Solution

Remove the scopes.

crates/bevy_app/src/app.rs

@@ -849,10 +849,8 @@ impl App {
     /// See [`bevy_reflect::TypeRegistry::register`].
     #[cfg(feature = "bevy_reflect")]
     pub fn register_type<T: bevy_reflect::GetTypeRegistration>(&mut self) -> &mut Self {
-        {
-            let registry = self.world.resource_mut::<AppTypeRegistry>();
-            registry.write().register::<T>();
-        }
+        let registry = self.world.resource_mut::<AppTypeRegistry>();
+        registry.write().register::<T>();
         self
     }
 
@@ -882,10 +880,8 @@ impl App {
     >(
         &mut self,
     ) -> &mut Self {
-        {
-            let registry = self.world.resource_mut::<AppTypeRegistry>();
-            registry.write().register_type_data::<T, D>();
-        }
+        let registry = self.world.resource_mut::<AppTypeRegistry>();
+        registry.write().register_type_data::<T, D>();
         self
     }