FEATURE: Promote bookmarks with reminders to core functionality (#9369)

The main thrust of this PR is to take all the conditional checks based on the `enable_bookmarks_with_reminders` away and only keep the code from the `true` path, making bookmarks with reminders the core bookmarks feature. There is also a migration to create `Bookmark` records out of `PostAction` bookmarks for a site.

### Summary

* Remove logic based on whether enable_bookmarks_with_reminders is true. This site setting is now obsolete, the old bookmark functionality is being removed. Retain the setting and set the value to `true` in a migration.
* Use the code from the rake task to create a database migration that creates bookmarks from post actions.
* Change the bookmark report to read from the new table.
* Get rid of old endpoints for bookmarks
* Link to the new bookmarks list from the user summary page

spec/lib/bookmark_reminder_notification_handler_spec.rb

@@ -8,7 +8,6 @@ RSpec.describe BookmarkReminderNotificationHandler do
   fab!(:user) { Fabricate(:user) }
 
   before do
-    SiteSetting.enable_bookmarks_with_reminders = true
     Discourse.redis.flushall
   end
 
@@ -89,17 +88,6 @@ RSpec.describe BookmarkReminderNotificationHandler do
       end
     end
 
-    context "when enable bookmarks with reminders is disabled" do
-      before do
-        SiteSetting.enable_bookmarks_with_reminders = false
-      end
-
-      it "does nothing" do
-        BrowserDetection.expects(:device).never
-        send_reminder
-      end
-    end
-
     def send_reminder
       subject.send_at_desktop_reminder(user: user, request_user_agent: user_agent)
     end