Simplify tracing-subscriber initialization (#128)

examples/multipart_form.rs

@@ -16,9 +16,7 @@ async fn main() {
     if std::env::var("RUST_LOG").is_err() {
         std::env::set_var("RUST_LOG", "multipart_form=debug,tower_http=debug")
     }
-    tracing_subscriber::fmt::fmt()
-        .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
-        .init();
+    tracing_subscriber::fmt::init();
 
     // build our application with some routes
     let app = route("/", get(show_form).post(accept_form))