Use Drop instead of destroy() for locks.

library/std/src/sys/itron/condvar.rs

@@ -117,8 +117,6 @@ impl Condvar {
         unsafe { mutex.lock() };
         success
     }
-
-    pub unsafe fn destroy(&self) {}
 }
 
 mod waiter_queue {

library/std/src/sys/itron/mutex.rs

@@ -64,8 +64,10 @@ impl Mutex {
             }
         }
     }
+}
 
-    pub unsafe fn destroy(&self) {
+impl Drop for Mutex {
+    fn drop(&mut self) {
         if let Some(mtx) = self.mtx.get().map(|x| x.0) {
             expect_success_aborting(unsafe { abi::del_mtx(mtx) }, &"del_mtx");
         }