Revert "mm: oom_kill: reap memory of a task that receives SIGKILL"

This reverts commit 724adb44.

Reason for revert: The changes introduced in this commit are causing an
undesirable SELinux denial as a side-effect. Additionally, it appears
(http://b/130391762

) that we do not enable the functionality that this
commit adds. Reverting the commit fixes the SELinux denial bug.

Bug: 138594811
Change-Id: Ie440e290dc89b72c46de2194da0275910c03a66d
Signed-off-by: Ashwini Oruganti <ashfall@google.com>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>