Remove unused futures-util features

Cf. #52.

Author: onalante-msft

Cargo.toml

@@ -11,7 +11,7 @@ readme = "README.md"
 edition = "2018"
 
 [dependencies]
-futures-util = "0.3"
+futures-util = { version = "0.3", default-features = false, features = ["alloc"] }
 hex = "0.4"
 hyper = "0.14"
 tokio = { version = "1.0", features = ["net"] }