Revert "cgroup: Use open-time credentials for process migraton perm checks"

commit bcb864df35d751a77abcfa116ae9d801f47a6e5b from
https://github.com/altera-opensource/linux-socfpga.git

This reverts commit 31f58fc8d843cfc1d458fa01f4c24c4ea37834e5. Due to a
mistake in resolving a merge conflict, this patch needs to get reverted.

Signed-off-by: Dinh Nguyen <dinh.nguyen@intel.com>
Signed-off-by: Wenlin Kang <wenlin.kang@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>