*: Replace _serde with dep:serde in Cargo.toml (#2868)

core/src/lib.rs

@@ -35,9 +35,6 @@
 //!   define how to upgrade each individual substream to use a protocol.
 //!   See the `upgrade` module.
 
-#[cfg(feature = "serde")]
-extern crate _serde as serde;
-
 #[allow(clippy::derive_partial_eq_without_eq)]
 mod keys_proto {
     include!(concat!(env!("OUT_DIR"), "/keys_proto.rs"));

core/src/peer_id.rs

@@ -183,7 +183,7 @@ impl From<PeerId> for Vec<u8> {
 impl Serialize for PeerId {
     fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
     where
-        S: _serde::Serializer,
+        S: serde::Serializer,
     {
         if serializer.is_human_readable() {
             serializer.serialize_str(&self.to_base58())