Revert "Deprecate collection_cache_key which is private API"

This reverts commit f656bb301a.

Reason: Test in Action View expects the `collection_cache_key` working...

ff6b713f5e/actionview/test/activerecord/relation_cache_test.rb (L21)
ff6b713f5e/actionview/test/fixtures/project.rb (L6)

https://buildkite.com/rails/rails/builds/60609#d19181fb-fe80-4d1e-891c-1109b540fb4b/981-1009

activerecord/lib/active_record/integration.rb

@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
 require "active_support/core_ext/string/filters"
-require "active_support/deprecation"
 
 module ActiveRecord
   module Integration
@@ -165,7 +164,6 @@ module ActiveRecord
       def collection_cache_key(collection = all, timestamp_column = :updated_at) # :nodoc:
         collection.send(:compute_cache_key, timestamp_column)
       end
-      deprecate :collection_cache_key
     end
 
     private

activerecord/lib/active_record/relation.rb

@@ -310,7 +310,7 @@ module ActiveRecord
     #   Product.where("name like ?", "%Game%").cache_key(:last_reviewed_at)
     def cache_key(timestamp_column = :updated_at)
       @cache_keys ||= {}
-      @cache_keys[timestamp_column] ||= compute_cache_key(timestamp_column)
+      @cache_keys[timestamp_column] ||= klass.collection_cache_key(self, timestamp_column)
     end
 
     def compute_cache_key(timestamp_column = :updated_at) # :nodoc:

activerecord/test/cases/collection_cache_key_test.rb

@@ -13,9 +13,7 @@ module ActiveRecord
     fixtures :developers, :projects, :developers_projects, :topics, :comments, :posts
 
     test "collection_cache_key on model" do
-      assert_deprecated do
-        assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, Developer.collection_cache_key)
-      end
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, Developer.collection_cache_key)
     end
 
     test "cache_key for relation" do