Move away from deprecated "_data" column.

As part of the new privacy work in Q, apps no longer have access to
raw filesystem paths, since they may live outside of the current
sandbox.  Instead, we need to use CR.openFileDescriptor().

Bug: 111960973
Test: builds, boots
Change-Id: I6e52a7dcb39850d9835183c44f5f638a5bf77202