Revert "rcu-tasks: Eliminate deadlocks involving do_exit() and RCU tasks"

This reverts commit d89abc4f which is
commit 1612160b upstream.

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

Bug: 161946584
Change-Id: I171efb67a0ccd090a3c655230d9f1b22729ba31b
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>