zephyr: work: Remove debug 'Sync' implementation

The WorkWaker now really does implement Sync, as we use an Arc and Mutex
to protect it.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

zephyr/src/work.rs

@@ -439,10 +439,6 @@ pub mod futures {
     // SAFETY: The worker struct is explicitly safe to send by the Zephyr docs.
     unsafe impl Send for WorkWaker {}
 
-    // SAFETY: The work is _not_ actually Sync, and this needs to be fixed.  However, as long as the
-    // 'wake' method for WorkWaker panics, we can implement Sync.
-    unsafe impl Sync for WorkWaker {}
-
     impl Wake for Mutex<WorkWaker> {
         fn wake(this: Arc<Self>) {
             // At this point, it isn't safe to implement a delayed waker because delayed wakers will