DEV: Enable unless cops

We discussed the use of `unless` internally and decided to enforce
available rules from rubocop to restrict its most problematic uses.

db/migrate/20210224162050_remove_emoji_one_from_emoji_set_site_setting.rb

@@ -3,7 +3,7 @@
 class RemoveEmojiOneFromEmojiSetSiteSetting < ActiveRecord::Migration[6.0]
   def up
     result = execute("SELECT value FROM site_settings WHERE name='emoji_set' and value='emoji_one'")
-    return unless result.count > 0
+    return if result.count.zero?
 
     execute "DELETE FROM site_settings where name='emoji_set' and value='emoji_one'"
     execute "UPDATE posts SET baked_version = 0 WHERE cooked LIKE '%/images/emoji/emoji_one%'"