chainHead/tests: Fix clippy (#2325)

Remove the genesis hash from tests:
- Clippy was passing on the PR:
https://github.com/paritytech/polkadot-sdk/pull/2296
- Clippy fails on master:
https://gitlab.parity.io/parity/mirrors/polkadot-sdk/-/jobs/4328487

This was a race with merging:
https://github.com/paritytech/polkadot-sdk/pull/2295, which introduced
another test that used the `CHAIN_GENESIS`

Signed-off-by: Alexandru Vasile <alexandru.vasile@parity.io>

substrate/client/rpc-spec-v2/src/chain_head/tests.rs

@@ -1627,7 +1627,6 @@ async fn follow_with_multiple_unpin_hashes() {
 		client.clone(),
 		backend,
 		Arc::new(TaskExecutor::default()),
-		CHAIN_GENESIS,
 		ChainHeadConfig {
 			global_max_pinned_blocks: MAX_PINNED_BLOCKS,
 			subscription_max_pinned_duration: Duration::from_secs(MAX_PINNED_SECS),