stream: move Elapsed to the root

Moved the Elapsed error to the root, un-deprecating it.

Ref: #6656

tokio-stream/src/lib.rs

@@ -95,7 +95,8 @@ pub mod adapters {
 cfg_time! {
     #[deprecated = "Import those symbols from adapters instead"]
     #[doc(hidden)]
-    pub use stream_ext::timeout::{Elapsed, Timeout};
+    pub use stream_ext::timeout::Timeout;
+    pub use stream_ext::timeout::Elapsed;
 }
 
 mod empty;