migrate: remove QMP/HMP commands for speed, downtime and cache size

migrate: remove QMP/HMP commands for speed, downtime and cache size

The generic 'migrate_set_parameters' command handle all types of param.

Only the QMP commands were documented in the deprecations page, but the
rationale for deprecating applies equally to HMP, and the replacements
exist. Furthermore the HMP commands are just shims to the QMP commands,
so removing the latter breaks the former unless they get re-implemented.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>