memguard: drop memguard_init() entirely

memguard: drop memguard_init() entirely

The use of MAP_SMALL_PAGES causes shattering of the superpages making up the
Xen virtual region, and is counter to the purpose of this series.
Furthermore, it is not required for the memguard infrastructure to function
(which itself uses map_pages_to_xen() for creating holes).

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <JBeulich@suse.com>
Acked-by: Stefano Stabellini <stefano.stabellini@citrix.com>