multifd: Drop x-multifd-page-count parameter

multifd: Drop x-multifd-page-count parameter

Libvirt don't want to expose (and explain it).  From now on we measure
the number of packages in bytes instead of pages, so it is the same
independently of architecture.  We choose the page size of x86.
Notice that in the following patch we make this variable.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>