Update scripts to reference contributors.json instead of committers.py in messaging

Update scripts to reference contributors.json instead of committers.py in messaging
https://bugs.webkit.org/show_bug.cgi?id=119342

Reviewed by Ryosuke Niwa.

Change the scripts to point people to contributors.json instead of
committers.py since the latter no longer contains the list of
contributors.

* Scripts/webkitpy/common/config/committervalidator.py:
(CommitterValidator._contributors_json_path):
(CommitterValidator._flag_permission_rejection_message):
* Scripts/webkitpy/common/config/committervalidator_unittest.py:
(CommitterValidatorTest.test_flag_permission_rejection_message):
* Scripts/webkitpy/common/net/bugzilla/bugzilla.py:
(Bugzilla._commit_queue_flag):
* Scripts/webkitpy/common/watchlist/watchlistparser.py:
(WatchListParser._validate):
* Scripts/webkitpy/common/watchlist/watchlistparser_unittest.py:
(WatchListParserTest.test_cc_rule_with_invalid_email):
* Scripts/webkitpy/tool/bot/feeders_unittest.py:
* Scripts/webkitpy/tool/commands/queues_unittest.py:
* Scripts/webkitpy/tool/steps/validatereviewer.py:
(ValidateReviewer.run):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@153535 268f45cc-cd09-0410-ab3c-d52691b4dbfc