Remove duplicate asserts in test (#5648)

# Objective

While poking around the hierarchy code, I wondered why some asserts in tests were duplicated.
Some git blame later, I found out that commit ( 8eb0440 ) added already existing asserts while removing others.

## Solution

Remove the duplicated asserts.

Author: BorisBoutillier

crates/bevy_hierarchy/src/child_builder.rs

@@ -599,8 +599,6 @@ mod tests {
         );
         assert_eq!(*world.get::<Parent>(child3).unwrap(), Parent(parent));
         assert_eq!(*world.get::<Parent>(child4).unwrap(), Parent(parent));
-        assert_eq!(*world.get::<Parent>(child3).unwrap(), Parent(parent));
-        assert_eq!(*world.get::<Parent>(child4).unwrap(), Parent(parent));
 
         let remove_children = [child1, child4];
         {
@@ -641,9 +639,6 @@ mod tests {
         assert_eq!(*world.get::<Parent>(child1).unwrap(), Parent(parent));
         assert_eq!(*world.get::<Parent>(child2).unwrap(), Parent(parent));
 
-        assert_eq!(*world.get::<Parent>(child1).unwrap(), Parent(parent));
-        assert_eq!(*world.get::<Parent>(child2).unwrap(), Parent(parent));
-
         world.entity_mut(parent).insert_children(1, &entities[3..]);
         let expected_children: SmallVec<[Entity; 8]> = smallvec![child1, child3, child4, child2];
         assert_eq!(
@@ -652,8 +647,6 @@ mod tests {
         );
         assert_eq!(*world.get::<Parent>(child3).unwrap(), Parent(parent));
         assert_eq!(*world.get::<Parent>(child4).unwrap(), Parent(parent));
-        assert_eq!(*world.get::<Parent>(child3).unwrap(), Parent(parent));
-        assert_eq!(*world.get::<Parent>(child4).unwrap(), Parent(parent));
 
         let remove_children = [child1, child4];
         world.entity_mut(parent).remove_children(&remove_children);