metadata_lib: convert to python3 only

All users of these modules are python3 only already.

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

Change-Id: Ibf2c48bde4300ee4281ac4852c2fa6c0bd055dce
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/2658799
Tested-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: George Engelbrecht <engeg@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/lib/metadata_lib.py b/lib/metadata_lib.py
index 21146ee..03424a4 100644
--- a/lib/metadata_lib.py
+++ b/lib/metadata_lib.py
@@ -10,6 +10,7 @@
 import datetime
 import json
 import math
+import sys
 
 from chromite.lib import results_lib
 from chromite.lib import constants
@@ -17,6 +18,9 @@
 from chromite.lib import cros_logging as logging
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 class _DummyLock(object):
   """A Dummy clone of RLock that does nothing."""
   def acquire(self, blocking=1):
diff --git a/lib/metadata_lib_unittest b/lib/metadata_lib_unittest
deleted file mode 120000
index 72196ce..0000000
--- a/lib/metadata_lib_unittest
+++ /dev/null
@@ -1 +0,0 @@
-../scripts/wrapper.py
\ No newline at end of file
diff --git a/lib/metadata_lib_unittest.py b/lib/metadata_lib_unittest.py
index 65f4cb1..477117d 100644
--- a/lib/metadata_lib_unittest.py
+++ b/lib/metadata_lib_unittest.py
@@ -8,12 +8,16 @@
 from __future__ import print_function
 
 import multiprocessing
+import sys
 
 from chromite.lib import metadata_lib
 from chromite.lib import cros_test_lib
 from chromite.lib import parallel
 
 
+assert sys.version_info >= (3, 6), 'This module requires Python 3.6+'
+
+
 class MetadataTest(cros_test_lib.TestCase):
   """Tests the correctness of various metadata methods."""