MDL-52045 block_tags: Fix invalid has_config() declaration

As the settings.php has been removed in MDL-51132, the block should no
longer declare it has global configuration.

blocks/tags/block_tags.php

@@ -31,10 +31,6 @@ class block_tags extends block_base {
         return true;
     }
 
-    public function has_config() {
-        return true;
-    }
-
     public function applicable_formats() {
         return array('all' => true);
     }