hwid: Deletages the HWID reading/writing function to gooftool.

Both reading/writing the HWID string from/to firmware GBB is not
related to the HWID v3 framework, so this CL removes the related
functions in `cros.factory.hwid.v3.hwid_utils` and lets `hwid read`
and `hwid write` command just delegate the real work to gooftool.

TEST=manual test
BUG=chromium:769653

Change-Id: I6f45003ae7b143badbfeb0db8089db74c456cb05
Reviewed-on: https://chromium-review.googlesource.com/844439
Commit-Ready: Yong Hong <yhong@google.com>
Tested-by: Yong Hong <yhong@google.com>
Reviewed-by: Yilun Lin <yllin@chromium.org>
diff --git a/py/gooftool/commands.py b/py/gooftool/commands.py
index b9e7cce..97d5359 100755
--- a/py/gooftool/commands.py
+++ b/py/gooftool/commands.py
@@ -111,6 +111,14 @@
   print 'Wrote HWID: %r' % options.hwid
 
 
+@Command('read_hwid')
+def ReadHWID(options):
+  """Read the HWID string from GBB."""
+
+  logging.info('reading the hwid string')
+  print GetGooftool(options).ReadHWID()
+
+
 _project_cmd_arg = CmdArg(
     '--project', metavar='PROJECT',
     default=None, help='Project name to test.')
@@ -746,7 +754,7 @@
   and development purposes, please use `hwid` command.
   """
   db = GetGooftool(options).db
-  encoded_string = options.hwid or hwid_utils.GetHWIDString()
+  encoded_string = options.hwid or GetGooftool(options).ReadHWID()
   if options.probe_results:
     probed_results = hwid_utils.GetProbedResults(infile=options.probe_results)
   else: