Drop dontaudit sys_admin rule from installd.

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: I3822600a06c242764a94f9b67d9fcd6f599d3453
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>