Request server-side data deletion when user opts out of operation pattern collection

[fmarier]

Users can opt out of the collection of operational pattern traces by toggling the P3A setting to OFF. When that happens, we should send a ping to the Stats backend to delete the data associated with that collection_id.

This is the right thing to do from a privacy point of view, but also from a data point of view since these records would be incomplete (i.e. we should ignore these incomplete traces in any analysis).

[fmarier]

Additionally, once the server-side data has been deleted, we should remove the collection_id and related local state from the user's machine.