ACPI: APEI: GHES: Remove unused ghes_estatus_pool_size_request()

ghes_estatus_pool_size_request() is unused now, so remove it.

Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>