Fix unrelated warnings

Just two trivial compiler warnings that are unrelated to the changes
made here.

Author: tnull

lightning-net-tokio/src/lib.rs

@@ -189,7 +189,7 @@ impl Connection {
 			// our timeslice to another task we may just spin on this peer, starving other peers
 			// and eventually disconnecting them for ping timeouts. Instead, we explicitly yield
 			// here.
-			tokio::task::yield_now().await;
+			let _ = tokio::task::yield_now().await;
 		};
 		let writer_option = us.lock().unwrap().writer.take();
 		if let Some(mut writer) = writer_option {

lightning/src/ln/channelmanager.rs

@@ -7967,8 +7967,6 @@ mod tests {
 	use bitcoin::hashes::Hash;
 	use bitcoin::hashes::sha256::Hash as Sha256;
 	use bitcoin::secp256k1::{PublicKey, Secp256k1, SecretKey};
-	#[cfg(feature = "std")]
-	use core::time::Duration;
 	use core::sync::atomic::Ordering;
 	use crate::events::{Event, HTLCDestination, MessageSendEvent, MessageSendEventsProvider, ClosureReason};
 	use crate::ln::{PaymentPreimage, PaymentHash, PaymentSecret};