typing: induce pytype to use the standard `attr` instead of the vendored copy
What was previously happening with the vendored copy was that pytype would stub
out all(?) classes that were decorated with `@attr.s` as `Any`. After this, we
get a ton of classes defined, and numerous fields and methods now have proper
types.
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"phabricator.uri": "https://phab.mercurial-scm.org/",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}