python: Remove Python 2.7 compatibility code

We don't support Python 2.7 anymore. Remove glue code like the six
dependency and "from __future__" imports from gem5's standard library.

Change-Id: I71834c325f86ff0329b222be87794ead96081f05
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39584
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>

src/python/m5/util/__init__.py

@@ -37,14 +37,11 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-from __future__ import print_function
-
 import os
 import re
 import sys
 
-from six import string_types
-from six.moves import zip_longest
+from itertools import zip_longest
 
 from . import convert
 from . import jobfile
@@ -123,7 +120,7 @@ def compareVersions(v1, v2):
     def make_version_list(v):
         if isinstance(v, (list,tuple)):
             return v
-        elif isinstance(v, string_types):
+        elif isinstance(v, str):
             return list(map(lambda x: int(re.match('\d+', x).group()),
                             v.split('.')))
         else: