MDL-49385 block_base: Deprecate config_save function.

block_base->config_save is not used anywhere any more. If contributed plugins
rely on it, it makes no difference since it is not being called, if they do
something like $this->config_save or parent::config_save somewhere in their
block class instance, this will still work as deprecated function will handle
it.

blocks/moodleblock.class.php

@@ -343,10 +343,12 @@ class block_base {
      * Default behavior: save all variables as $CFG properties
      * You don't need to override this if you 're satisfied with the above
      *
+     * @deprecated since Moodle 2.9 MDL-49385 - Please use Admin Settings functionality to save block configuration.
      * @param array $data
      * @return boolean
      */
     function config_save($data) {
+        debugging('config_save($data) is deprecated, use Admin Settings functionality to save block configuration.', DEBUG_DEVELOPER);
         foreach ($data as $name => $value) {
             set_config($name, $value);
         }

blocks/upgrade.txt

@@ -4,6 +4,7 @@ information provided here is intended especially for developers.
 === 2.9 ===
 
 * The obsolete method preferred_width() was removed (it was not doing anything)
+* Deprecated block_base::config_save as is not called anywhere and should not be used.
 
 === 2.8 ===