Revert "mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race"

This reverts commit b7754d3a which is
commit 1013af4f 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: I4ab2bfd3613398f09052a7035716e980ebbebcf4
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>