message: more example fixes
diff: //! # Example
  //!
  //! ```no_run
  -//! use tokio_postgres::{NoTls, Error, Row};
  +//! use tokio_postgres::{NoTls, Error};
  //!
  //! # #[cfg(not(feature = "runtime"))] fn main() {}
  //! # #[cfg(feature = "runtime")]
  //! #[tokio::main] // By default, tokio_postgres uses the tokio crate as its runtime.
  //! async fn main() -> Result<(), Error> {
  //! // Connect to the database.
  -//! let (mut client, connection) =
  +//! let (client, connection) =
  //! tokio_postgres::connect("host=localhost user=postgres", NoTls).await?;
  //!
  //! // The connection object performs the actual communication with the database,
  