chore: remove the unused `--chain-import` flag #9988

Job	Run time
Build Ubuntu	5m 4s
Build MacOS	2m 49s
cargo-publish-dry-run	6m 13s
Forest CLI checks	6m 7s
Calibnet check	3m 9s
Snapshot export checks	9m 35s
Calibnet no discovery checks	2m 1s
Calibnet stateless mode check	1m 42s
Wallet tests	4m 6s
State migrations	4m 44s
Bootstrap checks - Forest	3m 8s
Bootstrap checks - Lotus	6m 18s
Calibnet eth mapping check	5m 48s
Calibnet kademlia checks	2m 6s
Calibnet RPC checks	11m 52s
db-migration-checks	12m 32s
db-migration-checks-car-db	4m 37s
Devnet checks	9m 30s
Calibnet snapshot parity checks	0s
	1h 41m 21s

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