vm_event: remove xc_mem_access_enable_emulate() and friends

vm_event: remove xc_mem_access_enable_emulate() and friends

xc_mem_access_enable_emulate() and xc_mem_access_disable_emulate()
are currently no-ops, that is all they do is set a flag that
nobody else checks. The user can already set the EMULATE flags in
the vm_event response if emulation is desired, and having an extra
check above that is not inherently safer, but it does complicate
(currenly unnecessarily) the API. This patch removes these
functions and the corresponding hypervisor code.

Signed-off-by: Razvan Cojocaru <rcojocaru@bitdefender.com>
Acked-by: Tamas K Lengyel <tamas@tklengyel.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>