Remove shadows

[IceSentry]

Grid shadows have been a pain to maintain and we don't use them internally so we decided to remove this code.

[github-actions]

bevy_infinite_grid - ✅

required	step	result	details
✓	Custom:	⏭	Logs
✓	cargo fmt --verbose --all -- --check	✅	Logs
✓	cargo check	✅	Logs
✓	cargo clippy -- -D warnings	✅	Logs
✓	cargo doc --no-deps	✅	Logs
	cargo deny check licenses	✅	Logs
	cargo deny check bans	✅	Logs
	cargo deny check advisories	✅	Logs
	cargo deny check sources	✅	Logs
	cargo machete	✅	Logs
✓	cargo test	✅	Logs
	cargo miri test	⏭	Logs
✓	cargo package	✅	Logs

Pushed by: IceSentry, Action: pull_request;
Run: 8575821200