sync: fix docs for Send/Sync bounds in broadcast (#5480)

tokio/src/sync/broadcast.rs

@@ -4,7 +4,7 @@
 //! A [`Sender`] is used to broadcast values to **all** connected [`Receiver`]
 //! values. [`Sender`] handles are clone-able, allowing concurrent send and
 //! receive actions. [`Sender`] and [`Receiver`] are both `Send` and `Sync` as
-//! long as `T` is also `Send` or `Sync` respectively.
+//! long as `T` is `Send`.
 //!
 //! When a value is sent, **all** [`Receiver`] handles are notified and will
 //! receive the value. The value is stored once inside the channel and cloned on