Delegate `uniq` to `records`

This fixes CI failure due to 48f3be8c.

`Enumerable#uniq` was introduced since Ruby 2.4. We should delegate
`uniq` to `records` explicitly.

And since b644964b `ActiveRecord::Relation` includes `Enumerable` so
delegating `map` is unneeded.

activerecord/lib/active_record/relation/delegation.rb

@@ -36,7 +36,7 @@ def inherited(child_class)
     # may vary depending on the klass of a relation, so we create a subclass of Relation
     # for each different klass, and the delegations are compiled into that subclass only.
 
-    delegate :to_xml, :encode_with, :length, :collect, :map, :each, :all?, :include?, :to_ary, :join,
+    delegate :to_xml, :encode_with, :length, :collect, :uniq, :each, :all?, :include?, :to_ary, :join,
              :[], :&, :|, :+, :-, :sample, :reverse, :compact, :in_groups, :in_groups_of,
              :to_sentence, :to_formatted_s, :as_json,
              :shuffle, :split, :index, to: :records