docs: remove incorrect comment

When a FQCN is given, it may search through all namespaces.
And the App namespace is prefered by default.

Author: kenjis

user_guide_src/source/models/model/001.php

@@ -14,7 +14,5 @@
 $userModel = model('UserModel', false);
 
 // Create shared instance with a supplied database connection.
-// When no namespace is given, it will search through all namespaces
-// the system knows about and attempts to locate the UserModel class.
 $db        = db_connect('custom');
 $userModel = model('UserModel', true, $db);