Element delete doesn't delete entries in Queue

[sfsmfc]

If you delete an entry faster as the queue can execute an index job, you run into an error "Element #9055834 (site #1) not found (type: craft\elements\Entry)", because the element doesn't exists anymore. The delete action should also delete index entries in the queue to prevent such an error.

Tasks to reproduce this error:

• set "runQueueAutomatically" to false in config/general.php
• create a new entry
• a new index entry will be pushed into queue
• delete this new entry
• execute the queue

I will look, if I could make a patch for this.

[sfsmfc]

Pull-Request #37 is ready for review.