Move get_node() to tree_node and replace all the custom classdefs/funcdefs.

jedi/evaluate/sys_path.py

@@ -167,7 +167,7 @@ def _check_module(module_context):
         return sys_path
 
     try:
-        possible_names = module_context.get_node().used_names['path']
+        possible_names = module_context.tree_node.used_names['path']
     except KeyError:
         # module.used_names is MergedNamesDict whose getitem never throws
         # keyerror, this is superfluous.