Revert "cgroup: Fix issues in allow_attach callback"

This reverts commit 43eac670.

Part of Chromium commit series:

CHROMIUM: remove Android's cgroup generic permissions checks

The implementation is utterly broken, resulting in all processes being
allows to move tasks between sets (as long as they have access to the
"tasks" attribute), and upstream is heading towards checking only
capability anyway, so let's get rid of this code.

BUG=b:31790445,chromium:647994
TEST=Boot android container, examine logcat

Signed-off-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/394967


Reviewed-by: Ricky Zhou <rickyz@chromium.org>
Reviewed-by: John Stultz <john.stultz@linaro.org>

Change-Id: Ie4b516571c06456927f4bb19e02b148b385b13fb
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>