Remove an unnecessary 'static bound in the impl of Debug for Mutex.

There is no reason to require T: 'static; the bound appears to be
a historical artifact.

src/libstd/sync/mutex.rs

@@ -311,7 +311,7 @@ fn drop(&mut self) {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized + fmt::Debug + 'static> fmt::Debug for Mutex<T> {
+impl<T: ?Sized + fmt::Debug> fmt::Debug for Mutex<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.try_lock() {
             Ok(guard) => write!(f, "Mutex {{ data: {:?} }}", &*guard),