util: drop a duplicate import

This was already imported several lines above.

Differential Revision: https://phab.mercurial-scm.org/D12421

mercurial/util.py

@@ -42,7 +42,6 b' from .pycompat import ('
     open,
     setattr,
 )
-from .node import hex
 from hgdemandimport import tracing
 from . import (
     encoding,