Fix remote device wipe to not hang.

The DPM seemed to always go through ExternalStorageFormatter to wipe the
device and SD card. For SD cards emulated on a fuse filesystem, this
seems to fail unless the device is wholly encrypted. Bypass
ExternalStorageFormatter in those cases and just wipe as normal.

Bug: 5458396
Change-Id: Iec759ef894c6bd3863cb4e7329f4de4584c60c1a