x86/shadow: drop CONFIG_HVM conditionals from sh_update_cr3()

x86/shadow: drop CONFIG_HVM conditionals from sh_update_cr3()

Now that we're not building multi.c anymore for 2 and 3 guest levels
when !HVM, there's no point in having these conditionals anymore. (As
somewhat a special case, the last of the removed conditionals really
builds on shadow_mode_external() always returning false when !HVM.) This
way the code becomes a tiny bit more readable.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>