chore: remove last traces of nix #5406

Job	Run time
build-nargo	2m 25s
build-noirc-abi	2m 36s
build-noir-wasm	3m 33s
build-acvm-js	2m 53s
noir-js-backend-barretenberg	48s
noirc_abi	45s
ACVM JS (Browser)	1m 23s
noir_codegen	58s
ACVM JS (Node.js)	37s
Noir JS	1m 24s
Integration Tests (Browser)	5m 8s
noir_wasm	1m 17s
Integration Tests (Node)	3m 40s
End	1s
	27m 28s

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