Remove testing benchmark tests from CI again since not stable

.travis.yml

@@ -20,7 +20,7 @@ script:
 - |
   cargo check &&
   cargo test &&
-  cargo test --benches &&
+  # cargo test --benches && # Not available on stable, makes travis CI unhappy.
   cargo test --release
   # cargo kcov --verbose --coveralls &&
   # bash <(curl -s https://codecov.io/bash)