Revert "mm: protect SPF handler against anon_vma changes"

This reverts commit ff6cfddf.

Bug: 128240262
Change-Id: I317785d46d335aab974e194e5ea0d744513baecd
Signed-off-by: Minchan Kim <minchan@google.com>
[dereference23: Forward port to msm-5.4]
Signed-off-by: Alexander Winkowski <dereference23@outlook.com>