Revert "Start locking down /data/media access."

Caused b/35926593 because ExternalStorageProvider needs raw
access to underlying devices that aren't mounted visibly, like
USB mass storage devices.

This reverts commit 53d64fc839ad79be28d783f0f14082310a647dd9.
diff --git a/data/etc/platform.xml b/data/etc/platform.xml
index 6248856..344f3c8 100644
--- a/data/etc/platform.xml
+++ b/data/etc/platform.xml
@@ -60,6 +60,7 @@
     </permission>
 
     <permission name="android.permission.WRITE_MEDIA_STORAGE" >
+        <group gid="media_rw" />
         <group gid="sdcard_rw" />
     </permission>