perf: remove redundant fallback cleanup

[mattsse]

similar as #13398

this scanned the fallback peers on every hash and cleaned up no longer connected peers.

this is entirely redundant because we only select active peers anyway

reth/crates/net/network/src/transactions/fetcher.rs

Lines 199 to 205 in 0e019f2

	let TxFetchMetadata { fallback_peers, .. } =
	self.hashes_fetch_inflight_and_pending_fetch.peek(&hash)?;
	for peer_id in fallback_peers.iter() {
	if self.is_idle(peer_id) && peers.contains_key(peer_id) {
	return Some(peer_id)
	}

so we don't need to do this

[rkrasiuk]

trust you that we don't need to do this, otherwise lgtm