As per bug 1487622, annotations have side effects on codegen, one of
which changes a leak signature that the wpt harness doesn't match
against its whitelist anymore.
Interestingly, while looking at the issue, I found multiple moz_*
annotations that weren't actually looked for by the clang plugin,
making them useless. Even more interestingly, removing them changes
codegen in such a way that the leak signature mentioned above is not
altered anymore.
Differential Revision: https://phabricator.services.mozilla.com/D5000