Fix clippy::unnecessary_cast warning

```
warning: casting to the same type is unnecessary (`usize` -> `usize`)
  --> futures-util/src/stream/stream/take.rs:57:37
   |
57 |         let lower = cmp::min(lower, self.remaining as usize);
   |                                     ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `self.remaining`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
   = note: `#[warn(clippy::unnecessary_cast)]` on by default

warning: casting to the same type is unnecessary (`usize` -> `usize`)
  --> futures-util/src/stream/stream/take.rs:60:28
   |
60 |             Some(x) if x < self.remaining as usize => Some(x),
   |                            ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `self.remaining`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast

warning: casting to the same type is unnecessary (`usize` -> `usize`)
  --> futures-util/src/stream/stream/take.rs:61:23
   |
61 |             _ => Some(self.remaining as usize),
   |                       ^^^^^^^^^^^^^^^^^^^^^^^ help: try: `self.remaining`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_cast
```

futures-util/src/stream/stream/take.rs

@@ -54,11 +54,11 @@ where
 
         let (lower, upper) = self.stream.size_hint();
 
-        let lower = cmp::min(lower, self.remaining as usize);
+        let lower = cmp::min(lower, self.remaining);
 
         let upper = match upper {
-            Some(x) if x < self.remaining as usize => Some(x),
-            _ => Some(self.remaining as usize),
+            Some(x) if x < self.remaining => Some(x),
+            _ => Some(self.remaining),
         };
 
         (lower, upper)