message: Remove superfluous use of the `async_trait` macro
  The `IntoResponse` trait does not have any async functions.
diff: @@ -257,7 +257,6 @@ private class ServerHttpBoundProtocolTraitImplGenerator(
  Output(#{O}),
  Error(#{E})
  }
  - ##[#{AsyncTrait}::async_trait]
  impl #{SmithyHttpServer}::response::IntoResponse for $outputName {
  fn into_response(self) -> #{SmithyHttpServer}::response::Response {
  $intoResponseImpl
  @@ -289,7 +288,6 @@ private class ServerHttpBoundProtocolTraitImplGenerator(
  rustTemplate(
  """
  pub(crate) struct $outputName(#{O});
  - ##[#{AsyncTrait}::async_trait]
  impl #{SmithyHttpServer}::response::IntoResponse for $outputName {
  fn into_response(self) -> #{SmithyHttpServer}::response::Response {
  $intoResponseImpl
  