MDL-69050 lang: Fix variables and methods names in curl_security_helper

The code has been using terms that were found exclusive and potentially
derogatory. Fixing the terms and making the variables and methods
consistent with the related admin settings.

lib/filelib.php

@@ -3018,7 +3018,7 @@ class curl {
     private $cookie   = false;
     /** @var bool tracks multiple headers in response - redirect detection */
     private $responsefinished = false;
-    /** @var security helper class, responsible for checking host/ports against blacklist/whitelist entries.*/
+    /** @var security helper class, responsible for checking host/ports against allowed/blocked entries.*/
     private $securityhelper;
     /** @var bool ignoresecurity a flag which can be supplied to the constructor, allowing security to be bypassed. */
     private $ignoresecurity;