message: tracing: remove duplicated pattern in event! macro
  Line [747 to 753](https://github.com/tokio-rs/tracing/blob/70ee64a96f84b90fb50aaf4a44af241df5ce284e/tracing/src/macros.rs#L747-L753) is identical with line [754 to 760](https://github.com/tokio-rs/tracing/blob/70ee64a96f84b90fb50aaf4a44af241df5ce284e/tracing/src/macros.rs#L754-L760) in `tracing/src/macros.rs`.
  This PR simply removes one of the duplicated patterns.
diff: @@ -751,13 +751,6 @@ macro_rules! event {
  { message = format_args!($($arg)+), $($fields)* }
  )
  );
  - ( $lvl:expr, { $($fields:tt)* }, $($arg:tt)+ ) => (
  - $crate::event!(
  - target: module_path!(),
  - $lvl,
  - { message = format_args!($($arg)+), $($fields)* }
  - )
  - );
  ($lvl:expr, $($k:ident).+ = $($field:tt)*) => (
  $crate::event!(
  target: module_path!(),
  