Update Tokio to use std::future. (#1120)

A first pass at updating Tokio to use `std::future`.

Implementations of `Future` from the futures crate are updated to implement
`Future` from std. Implementations of `Stream` are moved to a feature flag.

This commits disables a number of crates that have not yet been updated.

tokio-executor/tests/executor.rs

@@ -1,17 +1,20 @@
 #![deny(warnings, rust_2018_idioms)]
+#![feature(await_macro, async_await)]
 
-use futures::{self, future::lazy, Future};
 use tokio_executor::{self, DefaultExecutor};
 
+use std::future::Future;
+use std::pin::Pin;
+
 mod out_of_executor_context {
     use super::*;
     use tokio_executor::Executor;
 
     fn test<F, E>(spawn: F)
     where
-        F: Fn(Box<dyn Future<Item = (), Error = ()> + Send>) -> Result<(), E>,
+        F: Fn(Pin<Box<dyn Future<Output = ()> + Send>>) -> Result<(), E>,
     {
-        let res = spawn(Box::new(lazy(|| Ok(()))));
+        let res = spawn(Box::pin(async {}));
         assert!(res.is_err());
     }
 
@@ -19,10 +22,4 @@ mod out_of_executor_context {
     fn spawn() {
         test(|f| DefaultExecutor::current().spawn(f));
     }
-
-    #[test]
-    fn execute() {
-        use futures::future::Executor as FuturesExecutor;
-        test(|f| DefaultExecutor::current().execute(f));
-    }
 }