py3: don’t encode node.bin() argument

It accepts str and bytes.

hgext/git/gitutil.py

@@ -44,8 +44,6 b' def togitnode(n):'
 def fromgitnode(n):
     """Opposite of togitnode."""
     assert len(n) == 40
-    if pycompat.ispy3:
-        return bin(n.encode('ascii'))
     return bin(n)