Issue #1807266 by cam8001, barbun: Convert user_cancel_method() variable to CMI system.

...stics/lib/Drupal/statistics/Tests/StatisticsAdminTest.php

...lib/Drupal/system/Tests/Upgrade/SystemUpgradePathTest.php

...modules/system/tests/upgrade/drupal-7.system.database.php

core/modules/user/config/user.settings.yml

core/modules/user/lib/Drupal/user/Tests/UserCancelTest.php

core/modules/user/user.admin.inc

core/modules/user/user.install

core/modules/user/user.pages.inc