Remove the --filename option for rec and session commands

Most of it can be done by using variable interpolation in a shell e.g.:

  asciinema rec "${HOSTNAME}-${USER}-$(date +%s)-$$.cast"

Cargo.toml

@@ -44,8 +44,6 @@ tokio-tungstenite = { version = "0.26.2", features = ["rustls-tls-native-roots"]
 rustls = { version = "0.23.26", default-features = false, features = ["aws_lc_rs"] }
 sha2 = "0.10.8"
 tokio-util = "0.7.10"
-chrono = "0.4.38"
-hostname = "0.4.1"
 
 [build-dependencies]
 clap = { version = "4.5.37", features = ["derive"] }