system_app.te: Update obsolete comment about cgroups

The Settings app no longer appears to modify cgroup attributes and
schedtune is deprecated.

Test: grep -r -e processgroup -e sched_policy -e cgroup packages/apps/Settings
Change-Id: I9ce88be575f4bcbfc4d1c8a2164e8e7370f6a981
diff --git a/private/system_app.te b/private/system_app.te
index e0ed8c3..0b6ffe2 100644
--- a/private/system_app.te
+++ b/private/system_app.te
@@ -151,7 +151,7 @@
   proc_version
 }:file r_file_perms;
 
-# Settings app writes to /dev/stune/foreground/tasks.
+# Allow system apps to modify cgroup attributes and migrate processes
 allow system_app cgroup:file w_file_perms;
 allow system_app cgroup_v2:file w_file_perms;
 allow system_app cgroup_v2:dir w_dir_perms;