lavfi/dnn: modify dnn interface for removing native backend

Native backend will be removed in following commits, so change the
dnn interface and modify the error message in it first.

Signed-off-by: Ting Fu <ting.fu@intel.com>

libavfilter/dnn/dnn_interface.c

@@ -24,7 +24,6 @@
  */
 
 #include "../dnn_interface.h"
-#include "dnn_backend_native.h"
 #include "dnn_backend_tf.h"
 #include "dnn_backend_openvino.h"
 #include "libavutil/mem.h"
@@ -39,13 +38,6 @@ DNNModule *ff_get_dnn_module(DNNBackendType backend_type)
     }
 
     switch(backend_type){
-    case DNN_NATIVE:
-        dnn_module->load_model = &ff_dnn_load_model_native;
-        dnn_module->execute_model = &ff_dnn_execute_model_native;
-        dnn_module->get_result = &ff_dnn_get_result_native;
-        dnn_module->flush = &ff_dnn_flush_native;
-        dnn_module->free_model = &ff_dnn_free_model_native;
-        break;
     case DNN_TF:
     #if (CONFIG_LIBTENSORFLOW == 1)
         dnn_module->load_model = &ff_dnn_load_model_tf;
@@ -71,7 +63,7 @@ DNNModule *ff_get_dnn_module(DNNBackendType backend_type)
     #endif
         break;
     default:
-        av_log(NULL, AV_LOG_ERROR, "Module backend_type is not native or tensorflow\n");
+        av_log(NULL, AV_LOG_ERROR, "Module backend_type is not supported or enabled.\n");
         av_freep(&dnn_module);
         return NULL;
     }