docsrs cfg fixes (#1137)

* Remove unused attribute in axum-core

* Fix docs.rs package metadata for axum-extra

axum-core/src/lib.rs

@@ -46,7 +46,6 @@
 #![deny(unreachable_pub, private_in_public)]
 #![allow(elided_lifetimes_in_paths, clippy::type_complexity)]
 #![forbid(unsafe_code)]
-#![cfg_attr(docsrs, feature(doc_cfg))]
 #![cfg_attr(test, allow(clippy::float_cmp))]
 
 #[macro_use]

axum-extra/Cargo.toml

@@ -58,4 +58,4 @@ tower = { version = "0.4", features = ["util"] }
 
 [package.metadata.docs.rs]
 all-features = true
-rustdocflags = ["--cfg", "docsrs"]
+rustdoc-args = ["--cfg", "docsrs"]