Revert "bpf, cgroups: Fix cgroup v2 fallback on v1/v2 mixed mode"

This reverts commit cf002be3 which is
commit 8520e224 upstream.

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

Bug: 161946584
Change-Id: I631b92972f55d564be4bd3df66e9e544d9cb109e
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>