Rely on const generic big arrays for PartialEq in msgs

Implementation of standard traits on arrays longer than 32 elements
was shipped in rustc 1.47, which is below our MSRV of 1.48 and we
can use to remove some unnecessary manual implementation of
`PartialEq` on `OnionPacket`.

Author: TheBlueMatt

lightning/src/ln/msgs.rs

@@ -1703,18 +1703,6 @@ impl onion_utils::Packet for OnionPacket {
 	}
 }
 
-impl Eq for OnionPacket { }
-impl PartialEq for OnionPacket {
-	fn eq(&self, other: &OnionPacket) -> bool {
-		for (i, j) in self.hop_data.iter().zip(other.hop_data.iter()) {
-			if i != j { return false; }
-		}
-		self.version == other.version &&
-			self.public_key == other.public_key &&
-			self.hmac == other.hmac
-	}
-}
-
 impl fmt::Debug for OnionPacket {
 	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 		f.write_fmt(format_args!("OnionPacket version {} with hmac {:?}", self.version, &self.hmac[..]))