Update src/libcore/slice/mod.rs

Co-authored-by: Lukas Kalbertodt <lukas.kalbertodt@gmail.com>

Author: VillSnow

src/libcore/slice/mod.rs

@@ -2701,7 +2701,8 @@ impl<T> [T] {
                 right = mid;
             }
         }
-        return left;
+
+        left
     }
 }