DEV: Remove all code referencing at_desktop bookmark reminders (#9650)

We have found no need for these reminder types, so we are removing the code for them.

db/migrate/20200506044956_migrate_at_desktop_bookmark_reminders.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class MigrateAtDesktopBookmarkReminders < ActiveRecord::Migration[6.0]
+  def up
+    # reminder_type 0 is at_desktop, which is no longer valid
+    DB.exec(
+      <<~SQL, now: Time.zone.now
+        UPDATE bookmarks SET reminder_type = NULL, reminder_at = NULL, updated_at = :now
+        WHERE reminder_type = 0
+      SQL
+    )
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end