ANDROID: fix ABI breakage caused by adding union type in struct page

The patchset includes two additional fields along with lru in struct page
but they were all union so it shouldn't break change the semantic.
However, ABI is broken so this patch reverts the patchset since it
doesn't change runtime behavior difference. Just lose code readability.

Bug: 230899966
Signed-off-by: Minchan Kim <minchan@google.com>
Change-Id: I4eb1a55a9ca52794e136870bfddbd04175f1134b