fix double emitting of value_changed event in _on_value_change function

Author: RichardFrangenberg

NodeGraphQt/custom_widgets/properties_bin/custom_widget_vectors.py

@@ -38,7 +38,6 @@ def _on_value_change(self, value=None, index=None):
             if index is not None:
                 self._value[index] = value
             self.value_changed.emit(self.toolTip(), self._value)
-        self.value_changed.emit(self.toolTip(), self._value)
 
     def _update_items(self):
         if not isinstance(self._value, (list, tuple)):