remove extraneous __future__ imports

Author: a-detiste

nixio/data_frame.py

@@ -6,7 +6,6 @@
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted under the terms of the BSD License. See
 # LICENSE file in the root of the Project.
-from __future__ import (absolute_import, division, print_function)
 try:
     from collections.abc import Iterable
 except ImportError:

nixio/test/test_validator.py

@@ -1,4 +1,3 @@
-from __future__ import (absolute_import, division, print_function)
 import nixio as nix
 import numpy as np
 import os

nixio/validator.py

@@ -6,7 +6,6 @@
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted under the terms of the BSD License. See
 # LICENSE file in the root of the Project.
-from __future__ import (absolute_import, division, print_function)
 from .util import units
 from .dimension_type import DimensionType