Drop levelFrom=none from untrusted_app entry.

In the absence of any levelFrom= specifier, the default is none,
so this is unnecessary and conspicuous in contrast to all other
entries.  It came from switching our default of levelFrom=app
to levelFrom=none in AOSP rather than just dropping it.

Change-Id: Ia2f8c72200318ef66a1b6d6b6c117f8848441d7f
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>

seapp_contexts

@@ -39,7 +39,7 @@ user=system domain=system_app type=system_data_file
 user=bluetooth domain=bluetooth type=bluetooth_data_file
 user=nfc domain=nfc type=nfc_data_file
 user=radio domain=radio type=radio_data_file
-user=_app domain=untrusted_app type=app_data_file levelFrom=none
+user=_app domain=untrusted_app type=app_data_file
 user=_app seinfo=platform domain=platform_app type=platform_app_data_file
 user=_app seinfo=shared domain=shared_app type=platform_app_data_file
 user=_app seinfo=media domain=media_app type=platform_app_data_file