[lit][NFC] remove future statements for mandatory features in Python 3 (#199786)
This patch removes future statements from lit for features that are
mandatory in Python 3.0 and later.
Specifically, it removes future statements for
[`absolute_import`](https://docs.python.org/3/library/__future__.html#future__.absolute_import)
and
[`print_function`](https://docs.python.org/3/library/__future__.html#future__.print_function),
since both became mandatory in Python 3.0.