Since FlatViews are shared now and ASes not, this gets rid of
address_space_init_shareable().

This should cause no behavioural change.
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20170921085110.25598-17-aik@ozlabs.ru>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>