[CSM] Stop using xDS enabled server for CSM observability tests (#36725)

Closes #36725

COPYBARA_INTEGRATE_REVIEW=https://github.com/grpc/grpc/pull/36725 from yashykt:RemoveXdsEnabledServerFromCsmInterop 91f3120f07
PiperOrigin-RevId: 638313782

test/cpp/interop/xds_interop_server.cc

@@ -86,10 +86,9 @@ int main(int argc, char** argv) {
   if (enable_csm_observability) {
     observability = EnableCsmObservability();
   }
-  grpc::testing::RunServer(absl::GetFlag(FLAGS_secure_mode),
-                           enable_csm_observability, port, maintenance_port,
-                           hostname, absl::GetFlag(FLAGS_server_id),
-                           [](grpc::Server* /* unused */) {});
+  grpc::testing::RunServer(
+      absl::GetFlag(FLAGS_secure_mode), port, maintenance_port, hostname,
+      absl::GetFlag(FLAGS_server_id), [](grpc::Server* /* unused */) {});
 
   return 0;
 }

test/cpp/interop/xds_interop_server_lib.cc

@@ -226,9 +226,8 @@ absl::optional<grpc::Status> GetStatusForRpcBehaviorMetadata(
   return absl::nullopt;
 }
 
-void RunServer(bool secure_mode, bool enable_csm_observability, int port,
-               const int maintenance_port, absl::string_view hostname,
-               absl::string_view server_id,
+void RunServer(bool secure_mode, int port, const int maintenance_port,
+               absl::string_view hostname, absl::string_view server_id,
                const std::function<void(Server*)>& server_callback) {
   std::unique_ptr<Server> xds_enabled_server;
   std::unique_ptr<Server> server;
@@ -252,14 +251,11 @@ void RunServer(bool secure_mode, bool enable_csm_observability, int port,
                  .BuildAndStart();
     LOG(INFO) << "Maintenance server listening on 0.0.0.0:" << maintenance_port;
   } else {
-    // CSM Observability requires an xDS enabled server.
-    auto builder = enable_csm_observability
-                       ? std::make_unique<XdsServerBuilder>()
-                       : std::make_unique<ServerBuilder>();
-    maintenance_services.AddToServerBuilder(builder.get());
+    ServerBuilder builder;
+    maintenance_services.AddToServerBuilder(&builder);
     server = builder
-                 ->AddListeningPort(absl::StrCat("0.0.0.0:", port),
-                                    grpc::InsecureServerCredentials())
+                 .AddListeningPort(absl::StrCat("0.0.0.0:", port),
+                                   grpc::InsecureServerCredentials())
                  .RegisterService(&service)
                  .BuildAndStart();
     LOG(INFO) << "Server listening on 0.0.0.0:" << port;

test/cpp/interop/xds_interop_server_lib.h

@@ -30,9 +30,8 @@ namespace testing {
 absl::optional<grpc::Status> GetStatusForRpcBehaviorMetadata(
     absl::string_view header_value, absl::string_view hostname);
 
-void RunServer(bool secure_mode, bool enable_csm_observability, int port,
-               const int maintenance_port, absl::string_view hostname,
-               absl::string_view server_id,
+void RunServer(bool secure_mode, int port, const int maintenance_port,
+               absl::string_view hostname, absl::string_view server_id,
                const std::function<void(Server*)>& server_callback);
 
 }  // namespace testing

test/cpp/interop/xds_interop_server_test.cc

@@ -37,9 +37,8 @@ namespace {
 
 void ServerLoop(int port, grpc_core::Mutex* mutex,
                 grpc_core::CondVar* condition, Server** server) {
-  RunServer(false, /*enable_csm_observability=*/false, port,
-            /* should not be used */ -1, "127.0.0.1", "test_server",
-            [&](Server* s) {
+  RunServer(false, port, /* should not be used */ -1, "127.0.0.1",
+            "test_server", [&](Server* s) {
               grpc_core::MutexLock lock(mutex);
               *server = s;
               condition->Signal();