hook_update_last_removed()
Return a number which is no longer available as hook_update_N().
If you remove some update functions from your mymodule.install file, you should notify Drupal of those missing functions. This way, Drupal can ensure that no update is accidentally skipped.
Implementations of this hook should be placed in a mymodule.install file in the same directory as mymodule.module.
Return value
An integer, corresponding to hook_update_N() which has been removed from mymodule.instal