nebraska_wrapper: convert to python3 only

All users of these modules are python3 only already.

BUG=chromium:997354
TEST=`./run_tests` passes

Change-Id: I8051fa982fe3645248b0a12451c6973389b5cf3c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2643375
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/lib/nebraska_wrapper.py b/lib/nebraska_wrapper.py
index 54f1a5c..359f935 100644
--- a/lib/nebraska_wrapper.py
+++ b/lib/nebraska_wrapper.py
@@ -13,6 +13,7 @@
 import shutil
 import multiprocessing
 import subprocess
+import sys
 
 from six.moves import urllib
 
@@ -26,6 +27,9 @@
 from chromite.lib import timeout_util
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 NEBRASKA_FILENAME = 'nebraska.py'
 
 # Error msg in loading shared libraries when running python command.
diff --git a/lib/nebraska_wrapper_unittest b/lib/nebraska_wrapper_unittest
deleted file mode 120000
index 72196ce..0000000
--- a/lib/nebraska_wrapper_unittest
+++ /dev/null
@@ -1 +0,0 @@
-../scripts/wrapper.py
\ No newline at end of file
diff --git a/lib/nebraska_wrapper_unittest.py b/lib/nebraska_wrapper_unittest.py
index 550dde1..c941fa9 100644
--- a/lib/nebraska_wrapper_unittest.py
+++ b/lib/nebraska_wrapper_unittest.py
@@ -10,6 +10,7 @@
 import multiprocessing
 import os
 import subprocess
+import sys
 
 import mock
 
@@ -23,6 +24,9 @@
 from chromite.lib import timeout_util
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 # pylint: disable=protected-access
 class RemoteNebraskaWrapperTest(cros_test_lib.MockTempDirTestCase):
   """A class for testing RemoteNebraskaWrapper."""