Remove all possible traces of grpc::experimental for callback API (#26584)

include/grpcpp/impl/codegen/client_callback.h

@@ -1226,32 +1226,5 @@ class ClientCallbackUnaryFactory {
 };
 
 }  // namespace internal
-
-// TODO(vjpai): Remove namespace experimental when de-experimentalized fully.
-namespace experimental {
-
-template <class Response>
-using ClientCallbackReader = ::grpc::ClientCallbackReader<Response>;
-
-template <class Request>
-using ClientCallbackWriter = ::grpc::ClientCallbackWriter<Request>;
-
-template <class Request, class Response>
-using ClientCallbackReaderWriter =
-    ::grpc::ClientCallbackReaderWriter<Request, Response>;
-
-template <class Response>
-using ClientReadReactor = ::grpc::ClientReadReactor<Response>;
-
-template <class Request>
-using ClientWriteReactor = ::grpc::ClientWriteReactor<Request>;
-
-template <class Request, class Response>
-using ClientBidiReactor = ::grpc::ClientBidiReactor<Request, Response>;
-
-typedef ::grpc::ClientUnaryReactor ClientUnaryReactor;
-
-}  // namespace experimental
-
 }  // namespace grpc
 #endif  // GRPCPP_IMPL_CODEGEN_CLIENT_CALLBACK_H

include/grpcpp/impl/codegen/server_callback.h

@@ -783,20 +783,13 @@ using UnimplementedBidiReactor =
 
 }  // namespace internal
 
-// TODO(vjpai): Remove namespace experimental when de-experimentalized fully.
+// TODO(vjpai): Remove namespace experimental when last known users are migrated
+// off.
 namespace experimental {
 
-template <class Request>
-using ServerReadReactor = ::grpc::ServerReadReactor<Request>;
-
-template <class Response>
-using ServerWriteReactor = ::grpc::ServerWriteReactor<Response>;
-
 template <class Request, class Response>
 using ServerBidiReactor = ::grpc::ServerBidiReactor<Request, Response>;
 
-using ServerUnaryReactor = ::grpc::ServerUnaryReactor;
-
 }  // namespace experimental
 
 }  // namespace grpc