Remove async tests

test/metabase/api/async_test.clj

-(ns metabase.api.async-test
-  "Tests for /api/async endpoints."
-  (:require [expectations :refer :all]
-            [metabase.test.async :refer [result!]]
-            [metabase.test.data :refer :all]
-            [metabase.test.data.users :refer :all]))
-
-(expect
-  true
-  (-> ((user->client :rasta) :get 200 (str "x-ray/field/" (id :venues :price)))
-      :job-id
-      number?))
-
-(expect
-  true
-  (let [client (user->client :rasta)
-        job-id (:job-id (client :get 200 (str "x-ray/field/" (id :venues :price))))]
-    (result! job-id)
-    (-> (client :get 200 (str "async/" job-id))
-        :result
-        (contains? :features))))