fs: update to use std::future (#1269)

tokio-fs/src/remove_dir.rs

@@ -1,7 +1,10 @@
-use futures::{Future, Poll};
 use std::fs;
+use std::future::Future;
 use std::io;
 use std::path::Path;
+use std::pin::Pin;
+use std::task::Context;
+use std::task::Poll;
 
 /// Removes an existing, empty directory.
 ///
@@ -34,10 +37,9 @@ impl<P> Future for RemoveDirFuture<P>
 where
     P: AsRef<Path>,
 {
-    type Item = ();
-    type Error = io::Error;
+    type Output = io::Result<()>;
 
-    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+    fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Self::Output> {
         crate::blocking_io(|| fs::remove_dir(&self.path))
     }
 }