Before we were removing items individually from the queue. We now
directly use RabbitMQ's queue purging mechanism.
(imported from commit 62ab52c724c5a221b4c81a967154a4046a579f84)
This is useful in debugging when you just want to discard all the
messages in a queue because they have the wrong structure.
(imported from commit 8559ac74f11841430b4d0c801d5506ebcb74c3eb)