repo_manifest: drop Python 2 support

We're Python 3 only now, so clean this up.

BUG=None
TEST=CQ passes

Change-Id: I45f96075a81e3360152671691018d52da855d351
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3556526
Reviewed-by: Sloan Johnson <sloanjohnson@google.com>
Tested-by: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/loman.py b/scripts/loman.py
index 900e0f4..886846a 100644
--- a/scripts/loman.py
+++ b/scripts/loman.py
@@ -12,7 +12,6 @@
 from chromite.lib import cros_build_lib
 from chromite.lib import git
 from chromite.lib import osutils
-from chromite.lib import repo_manifest
 
 
 class LocalManifest(object):
@@ -65,8 +64,7 @@
     # Fix manifest tag text and tail.
     self.nodes.text = '\n  '
     self.nodes.tail = '\n'
-    return ElementTree.tostring(
-        self.nodes, encoding=repo_manifest.TOSTRING_ENCODING)
+    return ElementTree.tostring(self.nodes, encoding='unicode')
 
   def GetProjects(self):
     return list(self.nodes.findall('project'))