Factory reset: Always show the "delete media" checkbox

CM is usually installed with recoveries that preserve datamedia,
including our own, so the assumption that deleting data will also
clear personal media is wrong. Always show the checkbox that was
originally limited to removable media to let the user do a full
reset

Change-Id: I2764c9509cc9ec50a1be979d748341037660a5da
(cherry picked from commit 26435eae)