factory: Use `dict.items` instead of `six.iteritems`

`six.iteritems` is equivalent to `dict.items` in python3, so we can
migrate all of this.

BUG=chromium:999876
TEST=make test

Change-Id: I7218c416e694da41996ae3ace6ce23e6f9fcfb72
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/factory/+/2200487
Reviewed-by: Yilin Yang (kerker) <kerker@chromium.org>
Tested-by: Yilin Yang (kerker) <kerker@chromium.org>
Commit-Queue: Yilin Yang (kerker) <kerker@chromium.org>
diff --git a/py/utils/pygpt.py b/py/utils/pygpt.py
index 0f1d9a7..6e0e0de 100755
--- a/py/utils/pygpt.py
+++ b/py/utils/pygpt.py
@@ -40,8 +40,6 @@
 import sys
 import uuid
 
-from six import iteritems
-
 
 class StructError(Exception):
   """Exceptions in packing and unpacking from/to struct fields."""
@@ -285,7 +283,7 @@
       self.Zero()
 
     all_names = [f for f in self.__slots__]
-    for name, value in iteritems(kargs):
+    for name, value in kargs.items():
       if name not in all_names:
         raise GPTError('%s does not support keyword arg <%s>.' %
                        (type(self).__name__, name))
@@ -351,7 +349,7 @@
 
   def Update(self, **dargs):
     """Applies multiple values in current object."""
-    for name, value in iteritems(dargs):
+    for name, value in dargs.items():
       setattr(self, name, value)
 
   def Zero(self):
@@ -398,7 +396,7 @@
   }
   TYPE_GUID_FROM_NAME = dict(
       ('efi' if v.startswith('EFI') else v.lower().split()[-1], k)
-      for k, v in iteritems(TYPE_GUID_MAP))
+      for k, v in TYPE_GUID_MAP.items())
   TYPE_GUID_UNUSED = TYPE_GUID_FROM_NAME['unused']
   TYPE_GUID_CHROMEOS_KERNEL = TYPE_GUID_FROM_NAME['kernel']
   TYPE_GUID_LIST_BOOTABLE = [
@@ -969,7 +967,7 @@
   def DefineArgs(self, parser):
     """Defines all available commands to an argparser subparsers instance."""
     subparsers = parser.add_subparsers(help='Sub-command help.', dest='command')
-    for name, instance in sorted(iteritems(self.commands)):
+    for name, instance in sorted(self.commands.items()):
       parser = subparsers.add_parser(
           name, description=instance.__doc__,
           formatter_class=argparse.RawDescriptionHelpFormatter,