Remove uses of six and from __future__ imports as they are no longer needed. Change-Id: I8d6aae84d8192b301d541b8dc81275f4932f9f2f Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39756 Reviewed-by: Gabe Black <gabe.black@gmail.com> Reviewed-by: Jason Lowe-Power <power.jg@gmail.com> Tested-by: kokoro <noreply+kokoro@google.com>