chore!: Remove backend field from artifacts #1130

Job	Run time
build-noirc-abi	3m 23s
build-noir-wasm	5m 2s
build-nargo	2m 9s
build-acvm-js	3m 3s
ACVM JS (Browser)	2m 3s
ACVM JS (Node.js)	33s
noir_codegen	1m 8s
Noir JS	1m 29s
noir-js-backend-barretenberg	47s
noirc_abi	40s
noir_wasm	57s
Integration Tests	8m 51s
End	1s
	30m 6s

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