Remove dead futures2 code. (#538)

The futures 0.2 crate is not intended for widespread usage. Also, the
futures team is exploring the compat shim route.

If futures 0.3 support is added to Tokio 0.1, then a different
integration route will be explored, making the current code unhelpful.

tokio-current-thread/src/lib.rs

@@ -45,9 +45,6 @@ use std::rc::Rc;
 use std::sync::{atomic, mpsc, Arc};
 use std::time::{Duration, Instant};
 
-#[cfg(feature = "unstable-futures")]
-use futures2;
-
 /// Executes tasks on the current thread
 pub struct CurrentThread<P: Park = ParkThread> {
     /// Execute futures and receive unpark notifications.
@@ -410,13 +407,6 @@ impl tokio_executor::Executor for CurrentThread {
         self.borrow().spawn_local(future, false);
         Ok(())
     }
-
-    #[cfg(feature = "unstable-futures")]
-    fn spawn2(&mut self, _future: Box<futures2::Future<Item = (), Error = futures2::Never> + Send>)
-        -> Result<(), futures2::executor::SpawnError>
-    {
-        panic!("Futures 0.2 integration is not available for current_thread");
-    }
 }
 
 impl<P: Park> fmt::Debug for CurrentThread<P> {
@@ -699,23 +689,6 @@ impl tokio_executor::Executor for TaskExecutor {
     {
         self.spawn_local(future)
     }
-
-    #[cfg(feature = "unstable-futures")]
-    fn spawn2(&mut self, _future: Box<futures2::Future<Item = (), Error = futures2::Never> + Send>)
-        -> Result<(), futures2::executor::SpawnError>
-    {
-        panic!("Futures 0.2 integration is not available for current_thread");
-    }
-
-    fn status(&self) -> Result<(), SpawnError> {
-        CURRENT.with(|current| {
-            if current.spawn.get().is_some() {
-                Ok(())
-            } else {
-                Err(SpawnError::shutdown())
-            }
-        })
-    }
 }
 
 impl<F> Executor<F> for TaskExecutor