Entity removals are sometimes missed when using a fixed schedule

[DiSaber]

I've just started experiencing an issue where removed entities are still collidable and raycasts are still detecting them. My rapier plugin setup: RapierPhysicsPlugin::<NoUserData>::default().with_length_unit(1.0).in_schedule(FixedPostUpdate).
Attached is a video where I show the ramp in the main area and then enter a map (which removes all the main area's entities). As shown, the ramp is still collidable even though the entity has been removed. I just updated to the bevy 0.15 branch from the pr but I doubt that's the issue. It looks like this commit (src/plugin/plugin.rs line 219) removed the systems::sync_removals system from PostUpdate but as the comment states: "These must be in the main schedule currently so that they do not miss events." I think that line is likely the culprit and the simplest solution is to just add it back.

Youtube link (github won't let me upload video since it's >10mb): https://youtu.be/iyIRC7qQOSk

Workaround: Use with_default_system_setup(false) and configure the system sets manually, with systems::sync_removals in PostUpdate as before.

[Vrixyz]

Thanks for the report! Let me know if you're still having issues with #600 fix