Remove unused imports.

yangson/datamodel.py

@@ -8,7 +8,6 @@ from .instance import (EntryKeys, RootNode, InstancePath,
                        MemberName)
 from .schema import (BadSchemaNodeType, DataNode, InternalNode,
                      NonexistentSchemaNode, RawObject, SchemaNode)
-from .statement import Statement
 from .typealiases import *
 
 class DataModel:

yangson/instvalue.py

@@ -2,7 +2,6 @@
 
 from datetime import datetime
 from typing import List, Union
-from .datatype import *
 
 # Local type aliases