Revert "rcu-tasks: Maintain lists to eliminate RCU-tasks/do_exit() deadlocks"

This reverts commit 4e86206b which is
commit 6b70399f upstream.

It breaks the Android kernel build and can be brought back in the future
in an safe way if it is really needed.

Bug: 161946584
Change-Id: Ib0f6cf4f9c175bfeb6c93f35750c59b935d95e1b
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>