Remove unicode literals from code base

jedi/inference/gradual/annotation.py

@@ -53,7 +53,7 @@ def _infer_annotation_string(context, string, index=None):
     value_set = context.infer_node(node)
     if index is not None:
         value_set = value_set.filter(
-            lambda value: value.array_type == u'tuple'  # noqa
+            lambda value: value.array_type == 'tuple'  # noqa
                             and len(list(value.py__iter__())) >= index
         ).py__simple_getitem__(index)
     return value_set