selinux: Downgrade CMFM's domain

the filemanager doesn't need to be in platform_app. Put it in untrusted_app,
especially since it's a possible su client

Change-Id: I164853f2c8721d86b5b90677cb33032a3b491ff5
diff --git a/sepolicy/seapp_contexts b/sepolicy/seapp_contexts
index f39256a..bfad418 100644
--- a/sepolicy/seapp_contexts
+++ b/sepolicy/seapp_contexts
@@ -1 +1,2 @@
+user=_app seinfo=platform name=com.cyanogenmod.filemanager domain=untrusted_app type=app_data_file
 user=theme_man domain=system_app type=system_data_file