Only cleanup ASECs in external storage DO NOT MERGE

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.

(Cherry-pick of 93ecb38daded7583a4a61f4f22519bb7a8a8c154)

Bug: 6948035
Change-Id: Ib60727bd360caa32173797ff5b4e1e21fcf20054
2 files changed