Remove `Nat` #684

Job	Run time
check-changes	16s
ran-none	0s
start-nix-linux-aarch64-build-default-test / nix-linux-arm64	1h 4m 59s
start-nix-linux-x86-64-tests / nix-linux-x86	45m 25s
start-nix-linux-aarch64-cargo-build-test / nix-linux-arm64	43m 36s
start-macos-x86-64-tests / test-rust-macos-x86-64	16m 31s
start-roc-benchmarks / benchmark roc programs	10m 49s
start-nix-macos-apple-silicon-tests / nix-apple-silicon	32m 38s
start-ubuntu-x86-64-tests / test zig, rust, wasm...	12m 37s
start-windows-release-build-test / windows-release-build	13m 21s
start-windows-tests / windows-test-subset	30m 16s
ran-full	0s
finish	1s
	4h 30m 29s

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