message: flame: remove unused imports from README example
  ## Motivation
  While writing a component tracing example, I noticed that these imports
  were giving me `unused_imports` warnings. It seems they aren't necessary
  anymore.
  ## Solution
  I removed the unused imports in this example.
diff: @@ -48,9 +48,8 @@ of the `FlameLayer`, see the docs for [`FlushGuard`].
  ## Layer Setup
  ```rust
  -use std::{fs::File, io::BufWriter};
  use tracing_flame::FlameLayer;
  -use tracing_subscriber::{registry::Registry, prelude::*, fmt};
  +use tracing_subscriber::{prelude::*, fmt};
  fn setup_global_subscriber() -> impl Drop {
  let fmt_layer = fmt::Layer::default();
  