Simplify configuration tests to speed up most commands

[dalin-]

Way back when Config Split was first introduced (Drupal 8.0ish) you needed to run a different command to import config (drush config-split-import), but that went away somewhere around Drupal 8.3. We don't have any sites that old. Nor do we have any sites that don't use Configuration Management. We could speed things up by ripping out the checks for Config module, and Config Split module. Just assume that they are there.