Remove RequestParts::take_extensions (#699)

* Remove `RequestParts::take_extensions`

* fix out of date docs

* Remove RequestAlreadyExtracted and replace it with BodyAlreadyExtracted

* fix docs

* fix test

* Update axum-core/src/extract/mod.rs

Co-authored-by: Jonas Platte <[email protected]>

* Remove macro only used once

Co-authored-by: Jonas Platte <[email protected]>

axum-core/src/macros.rs

@@ -1,39 +1,4 @@
 macro_rules! define_rejection {
-    (
-        #[status = $status:ident]
-        #[body = $body:expr]
-        $(#[$m:meta])*
-        pub struct $name:ident;
-    ) => {
-        $(#[$m])*
-        #[derive(Debug)]
-        #[non_exhaustive]
-        pub struct $name;
-
-        #[allow(deprecated)]
-        impl $crate::response::IntoResponse for $name {
-            fn into_response(self) -> $crate::response::Response {
-                let mut res = http::Response::new($crate::body::boxed(http_body::Full::from($body)));
-                *res.status_mut() = http::StatusCode::$status;
-                res
-            }
-        }
-
-        impl std::fmt::Display for $name {
-            fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-                write!(f, "{}", $body)
-            }
-        }
-
-        impl std::error::Error for $name {}
-
-        impl Default for $name {
-            fn default() -> Self {
-                Self
-            }
-        }
-    };
-
     (
         #[status = $status:ident]
         #[body = $body:expr]