[NFC] Remove Python 2 imports from __future__ (#42086)

The `__future__` we relied on is now,  where the 3 specific things are
all included [since Python 3.0](https://docs.python.org/3/library/__future__.html):

* absolute_import
* print_function
* unicode_literals
* division

These import statements are no-ops and are no longer necessary.

test/ModuleInterface/ModuleCache/Inputs/check-is-new.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # check-is-new.py - a more-legible way to read a timestamp test than test(1)
 #

test/ModuleInterface/ModuleCache/Inputs/check-is-old.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # check-is-old.py - a more-legible way to read a timestamp test than test(1)
 #

test/ModuleInterface/ModuleCache/Inputs/make-old.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 #
 # make-old.py - /bin/touch that writes a constant "old" timestamp.
 #