Revert "mm/hugetlb: add hugetlb_folio_subpool() helpers"

This reverts commit 6a8af731 which is
commit 149562f7 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I2987d07bc7063ecb38b8565a2dbd943fdf251aa2
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>