chore!: Remove `add_file` and `file_reader` from FileManager #702

Job	Run time
build-acvm-js	3m 27s
build-noirc-abi	3m 41s
build-noir-wasm	5m 8s
build-nargo	2m 14s
source-resolver	32s
ACVM JS (Node.js)	17s
ACVM JS (Browser)	1m 19s
noirc_abi	32s
noir_codegen	40s
Noir JS	2m 16s
noir-js-backend-barretenberg	40s
noir_wasm	56s
Integration Tests	8m 35s
End	1s
	30m 18s

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