PyListModel: Fix mimeData implementation

Do not call base implementation. This never worked because the base
implementation stores the encoded `itemData` under the first value of
`mimeTypes` result which is then promptly overwritten by us.

Author: ales-erjavec

Orange/widgets/utils/itemmodels.py

@@ -11,7 +11,7 @@
 
 from AnyQt.QtCore import (
     Qt, QObject, QAbstractListModel, QAbstractTableModel, QModelIndex,
-    QItemSelectionModel, QT_VERSION
+    QItemSelectionModel, QMimeData, QT_VERSION
 )
 from AnyQt.QtCore import pyqtSignal as Signal
 from AnyQt.QtGui import QColor
@@ -752,15 +752,15 @@ def supportedDropActions(self):
         return self._supportedDropActions
 
     def mimeTypes(self):
-        return [self.MIME_TYPE] + list(QAbstractListModel.mimeTypes(self))
+        return [self.MIME_TYPE]
 
     def mimeData(self, indexlist):
         if len(indexlist) <= 0:
             return None
 
         items = [self[i.row()] for i in indexlist]
         itemdata = [self.itemData(i) for i in indexlist]
-        mime = QAbstractListModel.mimeData(self, indexlist)
+        mime = QMimeData()
         mime.setData(self.MIME_TYPE, b'see properties: _items, _itemdata')
         mime.setProperty('_items', items)
         mime.setProperty('_itemdata', itemdata)