nebraska: Remove six.moves modules

This CL completely migrates nebraska to Python 3.

BUG=b:186156191, b:186491865
TEST=./nebraska_unittest.py
TEST=python3 nebraska.py --runtime-root /tmp

Change-Id: I3d0aedae03157254d9323f1ba01986c96dc7eadd
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2853774
Tested-by: Amin Hassani <[email protected]>
Reviewed-by: Jae Hoon Kim <[email protected]>
Reviewed-by: Congbin Guo <[email protected]>
Commit-Queue: Amin Hassani <[email protected]>
2 files changed