Remove ACgroupController_getFlags to fix API breakage

Since ACgroupController_getFlags was introduced after LLNDK freeze it
causes media crashes due to missing symbol. Remove the new function and
re-implement cgroup controller detection to not require flags field but
instead check for its existence on the first access.

Bug: 135049992
Test: libcutils_test with and without CONFIG_CPUSETS enabled
Change-Id: I0220d6a926884dc22a7424d7d0a980c379c6f4eb
Merged-In: I0220d6a926884dc22a7424d7d0a980c379c6f4eb
Signed-off-by: Suren Baghdasaryan <surenb@google.com>