ACPI / APEI: remove the unused dead-code for SEA/NMI notification type

For the SEA notification, the two functions ghes_sea_add() and
ghes_sea_remove() are only called when CONFIG_ACPI_APEI_SEA
is defined. If not, it will return errors in the ghes_probe()
and not continue. If the probe is failed, the ghes_sea_remove()
also has no chance to be called. Hence, remove the unnecessary
handling when CONFIG_ACPI_APEI_SEA is not defined.

For the NMI notification, it has the same issue as SEA notification,
so also remove the unused dead-code for it.

Signed-off-by: Dongjiu Geng <gengdongjiu@huawei.com>
Tested-by: Tyler Baicar <tbaicar@codeaurora.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>