Cleanup: use disj instead of set/difference where appropriate [ci drivers]

src/metabase/driver/crate.clj

 (ns metabase.driver.crate
   (:require [clojure.java.jdbc :as jdbc]
-            [clojure.set :as set]
             [honeysql.core :as hsql]
             [metabase.driver :as driver]
             [metabase.driver.crate.util :as crate-util]
@@ -69,7 +68,7 @@
           :details-fields (constantly [{:name         "hosts"
                                         :display-name "Hosts"
                                         :default      "localhost:5432"}])
-          :features       (comp (u/rpartial set/difference #{:foreign-keys}) sql/features)})
+          :features       (comp (u/rpartial disj :foreign-keys) sql/features)})
   sql/ISQLDriver
   (merge (sql/ISQLDriverDefaultsMixin)
          {:connection-details->spec  (u/drop-first-arg crate-spec)

src/metabase/driver/mongo.clj

 (ns metabase.driver.mongo
   "MongoDB Driver."
-  (:require (clojure [set :as set]
-                     [string :as s])
+  (:require [clojure.string :as s]
             [clojure.tools.logging :as log]
             [cheshire.core :as json]
             (monger [collection :as mc]
@@ -116,7 +115,7 @@
 
 (defn- describe-database [database]
   (with-mongo-connection [^com.mongodb.DB conn database]
-    {:tables (set (for [collection (set/difference (mdb/get-collection-names conn) #{"system.indexes"})]
+    {:tables (set (for [collection (disj (mdb/get-collection-names conn) "system.indexes")]
                     {:schema nil, :name collection}))}))
 
 (defn- describe-table [database table]

test/metabase/db/metadata_queries_test.clj

 (ns metabase.db.metadata-queries-test
-  (:require [clojure.set :as set]
-            [expectations :refer :all]
+  (:require [expectations :refer :all]
             [metabase.db :as db]
             [metabase.db.metadata-queries :refer :all]
             (metabase.models [field :refer [Field]]
@@ -12,7 +11,7 @@
 
 ;; Redshift & Crate tests are randomly failing -- see https://github.com/metabase/metabase/issues/2767
 (def ^:private ^:const metadata-queries-test-engines
-  (set/difference  qp-test/non-timeseries-engines #{:redshift :crate}))
+  (disj qp-test/non-timeseries-engines :redshift :crate))
 
 ;; ### FIELD-DISTINCT-COUNT
 (datasets/expect-with-engines metadata-queries-test-engines

test/metabase/query_processor/parameters_test.clj

 (ns metabase.query-processor.parameters-test
   "Tests for *MBQL* parameter substitution."
-  (:require [clojure.set :as set]
-            (clj-time [core :as t]
+  (:require (clj-time [core :as t]
                       [format :as tf])
             [expectations :refer :all]
             [metabase.driver :as driver]
@@ -134,7 +133,7 @@
 ;;; +-------------------------------------------------------------------------------------------------------+
 
 ;; for some reason param substitution tests fail on Redshift & (occasionally) Crate so just don't run those for now
-(def ^:private ^:const params-test-engines (set/difference non-timeseries-engines #{:redshift :crate}))
+(def ^:private ^:const params-test-engines (disj non-timeseries-engines :redshift :crate))
 
 ;; check that date ranges work correctly
 (datasets/expect-with-engines params-test-engines

test/metabase/query_processor/sql_parameters_test.clj

 (ns metabase.query-processor.sql-parameters-test
-  (:require [clojure.set :as set]
-            [clj-time.core :as t]
+  (:require [clj-time.core :as t]
             [expectations :refer :all]
             (metabase [db :as db]
                       [driver :as driver])
@@ -362,7 +361,7 @@
 
 ;; as with the MBQL parameters tests Redshift and Crate fail for unknown reasons; disable their tests for now
 (def ^:private ^:const sql-parameters-engines
-  (set/difference (engines-that-support :native-parameters) #{:redshift :crate}))
+  (disj (engines-that-support :native-parameters) :redshift :crate))
 
 (defn- process-native {:style/indent 0} [& kvs]
   (qp/process-query