chore(tty): drop unused futures crate dep

backend.rs defines its own BoxFuture type alias
(Pin<Box<dyn Future + Send>>) using std::future::Future + futures_core,
so the futures crate is unused. Removes the dead dependency.

Cargo.lock

@@ -137,7 +137,6 @@ dependencies = [
  "alknet-core",
  "async-trait",
  "bytes",
- "futures",
  "futures-core",
  "serde",
  "serde_json",

crates/alknet-tty/Cargo.toml

@@ -19,7 +19,6 @@ local = []
 alknet-core = { path = "../alknet-core" }
 tokio = { version = "1", features = ["full"] }
 bytes = "1"
-futures = "0.3"
 futures-core = "0.3"
 tokio-stream = "0.1"
 serde = { version = "1", features = ["derive"] }