docs/misc: xen-command-line: Remove wrong statement from serrors=diverse

docs/misc: xen-command-line: Remove wrong statement from serrors=diverse

When serrors=diverse is selected by the user, we will only synchronize
the pending SErrors on entry to hypervisor from guest context and exit
from guest to hypervisor context.

We don't need synchronize SErrors between guest context switch as they
would be categorized to Hypervisor generated SErrors in any case.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Release-acked-by: Juergen Gross <jgross@suse.com>