message: Fix string_application instantiation
diff: @@ -70,8 +70,6 @@ typename Inspector::result_type inspect(Inspector& f,
  return f(meta::type_name("sa_header"), hdr.payload);
  }
  -struct end_application {};
  -
  class string_application {
  public:
  using header_type = string_application_header;
  @@ -199,16 +197,14 @@ CAF_TEST(receive) {
  sec::unavailable_or_would_block);
  CAF_MESSAGE("adding both endpoint managers");
  auto mgr1 = make_endpoint_manager(mpx, sys, policy::scribe{sockets.first},
  - stream_string_application<
  - string_application,
  - end_application>{sys, buf});
  + extend<string_application>::with<
  + stream_string_application>{sys, buf});
  CAF_CHECK_EQUAL(mgr1->init(), none);
  mpx->handle_updates();
  CAF_CHECK_EQUAL(mpx->num_socket_managers(), 2u);
  auto mgr2 = make_endpoint_manager(mpx, sys, policy::scribe{sockets.second},
  - stream_string_application<
  - string_application,
  - end_application>{sys, buf});
  + extend<string_application>::with<
  + stream_string_application>{sys, buf});
  CAF_CHECK_EQUAL(mgr2->init(), none);
  mpx->handle_updates();
  CAF_CHECK_EQUAL(mpx->num_socket_managers(), 3u);
  