Remove mediaserver sysfs write permissions.

Mediaserver no longer appears, and maybe never did, need write
permission to sysfs files.
commit: 1de9c492 added auditing to
make sure this is the case, and such access has not been observed.
Remove the permissions and the associated auditallow rule to further
confine the mediaserver sandbox.

Bug: 22827371
Change-Id: I44ca1521b9791db027300aa84e54c074845aa735

mediaserver.te

@@ -35,8 +35,7 @@ set_prop(mediaserver, audio_prop)
 allow mediaserver audio_device:chr_file rw_file_perms;
 
 # XXX Label with a specific type?
-allow mediaserver sysfs:file rw_file_perms;
-auditallow mediaserver sysfs:file { write append };
+allow mediaserver sysfs:file r_file_perms;
 
 # Read resources from open apk files passed over Binder.
 allow mediaserver apk_data_file:file { read getattr };