Remove members only used by CDM8 from the IPDL and remove code that depended on
the removed IPDL. Rename various instances of 'error' to 'exception' as from
CDM9 'exception' is used exclusively to refer to promise failure states.
Depends on D5628
Differential Revision: https://phabricator.services.mozilla.com/D5629
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extra : moz-landing-system : lando