Only cleanup ASECs in external storage

Any ASEC or OBB files were unmounted when USB storage was set to UMS
mode. This changes it so only ASEC files on external storage and OBB
files mounted from external storage are unmounted.

Bug: 6948035
Change-Id: I91bc09ee5b792970b0eef895f6886f3ffad00e8f
2 files changed