parsers: remove unused dependency on util

Parsers.py had a reference to util.sha1 which was unused. This commit removes
this reference as well as the unused import of util to simplify the dependency
graph. This is important for the next commit which actually relocates part
of a module to eliminate a cycle.

mercurial/pure/parsers.py

@@ -6,14 +6,12 b''
 # GNU General Public License version 2 or any later version.
 
 from mercurial.node import nullid
-from mercurial import util
 import struct, zlib, cStringIO
 
 _pack = struct.pack
 _unpack = struct.unpack
 _compress = zlib.compress
 _decompress = zlib.decompress
-_sha = util.sha1
 
 # Some code below makes tuples directly because it's more convenient. However,
 # code outside this module should always use dirstatetuple.