chore: move enumerate test to correct location (#867)

tests/enumerate.rs

@@ -3,10 +3,6 @@ extern crate tokio;
 extern crate tokio_executor;
 extern crate tokio_timer;
 
-#[macro_use]
-mod support;
-
-use futures::prelude::*;
 use futures::sync::mpsc;
 use tokio::util::StreamExt;
 
@@ -22,7 +18,7 @@ fn enumerate() {
         }
     });
 
-    let mut result = rx.enumerate().collect();
+    let result = rx.enumerate().collect();
     assert_eq!(
         result.wait(),
         Ok(vec![(0, 0), (1, 2), (2, 4), (3, 6), (4, 8)])