Basic Pipelined-Rendering App has Excessive CPU Utilization

## Bevy version

Commit ID: `e8412df0`

## Operating system & version

Manjaro Linux with Nvidia proprietary drivers.

## What you did

I ran a very basic Pipelined rendering app on release mode.

```rs
use bevy::{
ecs::prelude::*,
prelude::{App},
PipelinedDefaultPlugins,
render2::{
camera::OrthographicCameraBundle
}
};

fn main() {
App::new().add_plugins(PipelinedDefaultPlugins)
.add_startup_system(setup_system)
.run();
}

fn setup_system(mut commands: Commands) {
commands.spawn_bundle(OrthographicCameraBundle::new_2d());
}
```

## What you expected to happen

This example code should in-theory run at near 0% CPU utilization.

## What actually happened

The CPU utilization was hovering around 1/3 usage.

## Additional information

The output of running `cargo-flamegraph`: [flamegraph.zip](https://github.com/bevyengine/bevy/files/7612810/flamegraph.zip)

I'm running an [Intel Core i7-9750H](https://www.intel.com/content/www/us/en/products/sku/191045/intel-core-i79750h-processor-12m-cache-up-to-4-50-ghz/specifications.html) with 16 GB of RAM.

This was the 2nd item that was logged (I thought it might be useful):
```
INFO bevy_render2::renderer: AdapterInfo { name: "NVIDIA GeForce GTX 1660 Ti", vendor: 4318, device: 8593, device_type: DiscreteGpu, backend: Vulkan }
```