Set sdcard as non-removable (workaround for mediaprovider bug)

Solves this bug:
https://github.com/LegacyXperia/local_manifests/issues/491

Might be a good idea for additional reasons:
* Unmounting a SD card via USB Settings does not unmount swap or sdext,
  which can cause physical damage/instability.
* When USB type is set as MTP (default), the SD card is not removable
  unless configuration is changed to UMS.