Deleted picklist values should not be hidden, but deleted

At the moment, we are keeping deleted picklist values in the database (just changing status to hidden) in order to keep this value on items where it was previously selected. Therefore API can still use them. Please update the functionality so that:

1) Removing a value from a picklist should fail if the value is in use;
2) If the value is not in use, it should be successfully removed;
3) Values not defined in the picklist cannot be used.

For future reference, please use CR-666058.