Fix: UI: Hide internal "mode" property in Mesh Edit Duplicate

Hides an internal "mode" property in the Edit Mode mesh "Add Duplicate"
operator Adjust Last Operation menu. Old UI issue noticed during the
Tablet Workshop.

Pull Request: https://projects.blender.org/blender/blender/pulls/144794

source/blender/editors/mesh/editmesh_tools.cc

@@ -2059,15 +2059,16 @@ void MESH_OT_duplicate(wmOperatorType *ot)
   ot->poll = ED_operator_editmesh;
 
   /* to give to transform */
-  RNA_def_int(ot->srna,
-              "mode",
-              blender::ed::transform::TFM_TRANSLATION,
-              0,
-              INT_MAX,
-              "Mode",
-              "",
-              0,
-              INT_MAX);
+  PropertyRNA *prop = RNA_def_int(ot->srna,
+                                  "mode",
+                                  blender::ed::transform::TFM_TRANSLATION,
+                                  0,
+                                  INT_MAX,
+                                  "Mode",
+                                  "",
+                                  0,
+                                  INT_MAX);
+  RNA_def_property_flag(prop, PROP_HIDDEN);
 }
 
 static BMLoopNorEditDataArray *flip_custom_normals_init_data(BMesh *bm)