Remove unnecessary clippy allows (#7768)

# Objective

I think that these allows are no longer necessary after #6534.

## Solution

Let's remove them and see if clippy complains.

crates/bevy_ecs/src/world/mod.rs

@@ -1763,8 +1763,6 @@ impl fmt::Debug for World {
     }
 }
 
-// TODO: remove allow on lint - https://github.com/bevyengine/bevy/issues/3666
-#[allow(clippy::non_send_fields_in_send_ty)]
 // SAFETY: all methods on the world ensure that non-send resources are only accessible on the main thread
 unsafe impl Send for World {}
 // SAFETY: all methods on the world ensure that non-send resources are only accessible on the main thread

crates/bevy_ui/src/flex/mod.rs

@@ -29,8 +29,6 @@ pub struct FlexSurface {
 }
 
 // SAFETY: as long as MeasureFunc is Send + Sync. https://github.com/DioxusLabs/taffy/issues/146
-// TODO: remove allow on lint - https://github.com/bevyengine/bevy/issues/3666
-#[allow(clippy::non_send_fields_in_send_ty)]
 unsafe impl Send for FlexSurface {}
 unsafe impl Sync for FlexSurface {}