MDL-39478 behat: New constant to detect when the test site is running

Also removing an unused var and method.

lib/behat/classes/util.php

@@ -250,7 +250,6 @@ class behat_util extends testing_util {
      * To check is the current script is running in the test
      * environment
      *
-     * @see tool_behat::is_using_test_environment()
      * @return bool
      */
     public static function is_test_mode_enabled() {
@@ -263,20 +262,6 @@ class behat_util extends testing_util {
         return false;
     }
 
-    /**
-     * Returns true if Moodle is currently running with the test database and dataroot
-     * @return bool
-     */
-    public static function is_using_test_environment() {
-        global $CFG;
-
-        if (!empty($CFG->originaldataroot)) {
-            return true;
-        }
-
-        return false;
-    }
-
     /**
      * Returns the path to the file which specifies if test environment is enabled
      * @return string