Remove workaround for deref issue that no longer exists.

The double underscores were used to work around issue rust-lang#12808, which was
solved in 2016.

library/std/src/sys_common/remutex.rs

@@ -37,9 +37,7 @@ impl<T> RefUnwindSafe for ReentrantMutex<T> {}
 /// guarded data.
 #[must_use = "if unused the ReentrantMutex will immediately unlock"]
 pub struct ReentrantMutexGuard<'a, T: 'a> {
- // funny underscores due to how Deref currently works (it disregards field
- // privacy).
- __lock: &'a ReentrantMutex<T>,
+ lock: &'a ReentrantMutex<T>,
 }
 
 impl<T> !marker::Send for ReentrantMutexGuard<'_, T> {}
@@ -129,23 +127,23 @@ impl<T: fmt::Debug + 'static> fmt::Debug for ReentrantMutex<T> {
 
 impl<'mutex, T> ReentrantMutexGuard<'mutex, T> {
  fn new(lock: &'mutex ReentrantMutex<T>) -> ReentrantMutexGuard<'mutex, T> {
- ReentrantMutexGuard { __lock: lock }
+ ReentrantMutexGuard { lock }
  }
 }
 
 impl<T> Deref for ReentrantMutexGuard<'_, T> {
  type Target = T;
 
  fn deref(&self) -> &T {
- &self.__lock.data
+ &self.lock.data
  }
 }
 
 impl<T> Drop for ReentrantMutexGuard<'_, T> {
  #[inline]
  fn drop(&mut self) {
  unsafe {
- self.__lock.inner.unlock();
+ self.lock.inner.unlock();
  }
  }
 }