Drop dontaudit sys_admin rule from rild.

Old Android kernels (e.g. kernel/goldfish android-2.6.29 commit 2bda29)
fell back to a CAP_SYS_ADMIN check even before checking uids if the cgroup
subsystem did not define its own can_attach handler.  This doesn't appear
to have ever been the case of mainline, and is not true of the 3.4 Android
kernels.  So we no longer need to dontaudit sys_admin to avoid log noise.

Change-Id: I2faade6665a4adad91472c95f94bd922a449b240
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>