Use the parser to check for certain namedtuple features

This fixes tests that are used with python 2 but a different environment

jedi/evaluate/imports.py

@@ -12,7 +12,6 @@ This module also supports import autocompletion, which means to complete
 statements like ``from datetim`` (curser at the end would return ``datetime``).
 """
 import os
-import sys
 
 from parso.python import tree
 from parso.tree import search_ancestor