Bug 1620923 - Avoid using `six` since it is not installed everywhere r=lth

This will eagerly generate all of the manifests and hold them all at once in memory, but only for Python 2. If that causes problems, we should complete the port to Python 3.

Differential Revision: https://phabricator.services.mozilla.com/D66090

--HG--
extra : moz-landing-system : lando

js/src/tests/lib/manifest.py

@@ -6,7 +6,6 @@ from __future__ import print_function
 
 import os
 import re
-import six
 import sys
 from subprocess import Popen, PIPE
 
@@ -259,7 +258,7 @@ def _emit_manifest_at(location, relative, test_gen, depth):
     filename = os.path.join(location, 'jstests.list')
     manifest = []
     numTestFiles = 0
-    for k, test_list in six.iteritems(manifests):
+    for k, test_list in manifests.items():
         fullpath = os.path.join(location, k)
         if os.path.isdir(fullpath):
             manifest.append("include " + k + "/jstests.list")