stop using dict iter* helpers

Change from iter{keys,items,values}() to {keys,items,values}().
Python 3 doesn't offer the iter variants, and we don't really have
any cases where performance is critical where we'd need to avoid
creating the temporary list (which is what Python 2 does).

This is mostly mechanical.

BUG=chromium:980619
TEST=lint is unchanged in chromite
TEST=unittests pass

Change-Id: I591110f2eb5d43bb9268b975b14bd7ade66a4e35
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/1689014
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Reviewed-by: David Burger <dburger@chromium.org>
diff --git a/scripts/cros_setup_toolchains.py b/scripts/cros_setup_toolchains.py
index ed9fc31..50f2148 100644
--- a/scripts/cros_setup_toolchains.py
+++ b/scripts/cros_setup_toolchains.py
@@ -585,7 +585,7 @@
 
   # Cleaning doesn't care about consistency and rebuilding package.* files.
   packages = []
-  for pkg, vers in unmergemap.iteritems():
+  for pkg, vers in unmergemap.items():
     packages.extend('=%s-%s' % (pkg, ver) for ver in vers if ver != '9999')
 
   if packages:
@@ -1036,7 +1036,7 @@
         link = sym_paths[elf]
         GeneratePathWrapper(output_dir, link, elf)
 
-    for lib, lib_data in e['libs'].iteritems():
+    for lib, lib_data in e['libs'].items():
       if lib in donelibs:
         continue