Revert "Subscription manager"

This reverts commit a612500b0f.

src/library/library.cr

@@ -42,25 +42,6 @@ class Library
         end
       end
     end
-
-    subscription_interval = Config.current
-      .mangadex["subscription_update_interval_hours"].as Int32
-    unless subscription_interval < 1
-      spawn do
-        loop do
-          subscriptions = Storage.default.subscriptions
-          Logger.info "Checking MangaDex for updates on " \
-                      "#{subscriptions.size} subscriptions"
-          added_count = 0
-          subscriptions.each do |sub|
-            added_count += sub.check_for_updates
-          end
-          Logger.info "Subscription update completed. Added #{added_count} " \
-                      "chapters to the download queue"
-          sleep subscription_interval.hours
-        end
-      end
-    end
   end
 
   def titles