chore: use ready macro from futures-core (#1300)

tokio-threadpool/src/blocking.rs

@@ -1,5 +1,6 @@
 use crate::worker::Worker;
 
+use futures_core::ready;
 use std::error::Error;
 use std::fmt;
 use std::task::Poll;

tokio-threadpool/src/lib.rs

@@ -131,15 +131,6 @@
 
 pub mod park;
 
-macro_rules! ready {
-    ($e:expr) => {
-        match $e {
-            ::std::task::Poll::Ready(t) => t,
-            ::std::task::Poll::Pending => return ::std::task::Poll::Pending,
-        }
-    };
-}
-
 mod blocking;
 mod builder;
 mod callback;