time: remove Unpin bound on Throttle methods (#5105)

tokio-stream/src/stream_ext/throttle.rs

@@ -4,7 +4,6 @@ use crate::Stream;
 use tokio::time::{Duration, Instant, Sleep};
 
 use std::future::Future;
-use std::marker::Unpin;
 use std::pin::Pin;
 use std::task::{self, Poll};
 
@@ -41,8 +40,7 @@ pin_project! {
     }
 }
 
-// XXX: are these safe if `T: !Unpin`?
-impl<T: Unpin> Throttle<T> {
+impl<T> Throttle<T> {
     /// Acquires a reference to the underlying stream that this combinator is
     /// pulling from.
     pub fn get_ref(&self) -> &T {