Simplify flush on drop for trace provider.

apollo-router/src/plugins/telemetry/mod.rs

@@ -100,17 +100,13 @@ impl Drop for Telemetry {
             // Tracer providers must be flushed. This may happen as part of otel if the provider was set
             // as the global, but may also happen in the case of an failed config reload.
             // If the tracer prover is present then it was not handed over so we must flush it.
-            // The magic incantation seems to be that the flush MUST happen within a tokio runtime,
-            // and then within a spawn blocking.
+            // The magic incantation seems to be that the flush MUST happen in a separate thread.
             ::tracing::debug!("flushing telemetry");
-            std::thread::spawn(|| {
-                let runtime = tokio::runtime::Builder::new_multi_thread().build().unwrap();
-                runtime.block_on(async {
-                    let jh = tokio::task::spawn_blocking(move || {
-                        opentelemetry::trace::TracerProvider::force_flush(&tracer_provider);
-                    });
-                    futures::executor::block_on(jh).expect("failed to flush tracer provider");
+            std::thread::spawn(|| async {
+                let jh = tokio::task::spawn_blocking(move || {
+                    opentelemetry::trace::TracerProvider::force_flush(&tracer_provider);
                 });
+                futures::executor::block_on(jh).expect("failed to flush tracer provider");
             });
         }