migration/i386: Remove support for pre-0.12 formats

Remove support for versions of the CPU state prior to 11
which is the version used in qemu 0.12 - you'd be pretty
lucky if you got a migration stream to work from anything
that old anyway.  This doesn't affect the machine type
definition in any way.

My main reason for doing this is the hack for sysenter_esp/eip
that uses .get/.put's in state versions less than 7 (that's
prior to somewhere before 0.10).

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170405190024.27581-4-dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
