Revert "mm/mremap: fix dup_anon_vma() in vma_merge() case 4"

This reverts commit 4c675996.

There are boot breaking mm changes and this too needs to be reverted and
will be fixed up soon.

Bug: 277214742
Cc: André Draszik <draszik@google.com>
Change-Id: I58ef056586ec27c98db69df8ab9d2634148f4449
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>