util: drop the 'unpacker' helper

It is not helping anything anymore.

mercurial/obsolete.py

@@ -299,7 +299,7 b' def _fm1purereadmarkers(data, off):'
 
     # Loop on markers
     stop = len(data) - _fm1fsize
-    ufixed = util.unpacker(_fm1fixed)
+    ufixed = struct.Struct(_fm1fixed).unpack
 
     while off <= stop:
         # read fixed part

mercurial/util.py

@@ -19,7 +19,7 b' import error, osutil, encoding, parsers'
 import errno, shutil, sys, tempfile, traceback
 import re as remod
 import os, time, datetime, calendar, textwrap, signal, collections
-import imp, socket, urllib, struct
+import imp, socket, urllib
 import gc
 
 if os.name == 'nt':
@@ -232,10 +232,6 b' except NameError:'
 import subprocess
 closefds = os.name == 'posix'
 
-def unpacker(fmt):
-    """create a struct unpacker for the specified format"""
-    return struct.Struct(fmt).unpack
-
 def popen2(cmd, env=None, newlines=False):
     # Setting bufsize to -1 lets the system decide the buffer size.
     # The default for bufsize is 0, meaning unbuffered. This leads to