Don't have Bevy resize to full-screen

Now that I have a custom canvas, Bevy should adopt that as it's render
target rather than further modifying it.

src/main.rs

@@ -11,7 +11,6 @@ fn main() {
         .add_plugins(DefaultPlugins.set(WindowPlugin {
             primary_window: Some(Window {
                 canvas: Some("#boids-canvas".to_owned()),
-                fit_canvas_to_parent: true,
                 prevent_default_event_handling: false,
                 ..default()
             }),