Revert "ExternalStorageProvider: use mount point in device list"

ActivityThread Start proc com.android.externalstorage for broadcast com.android.externalstorage/.MountReceiver: pid=3075 uid=10006 gids={50006, 1028, 1023, 1015}
AndroidRuntime Failed to find provider info for com.android.externalstorage.documents
AndroidRuntime Process com.android.externalstorage, PID:3075
AndroidRuntime java.lang.RuntimeException: Unable to start receiver com.android.externalstorage.MountReceiver: java.lang.NullPointerException at com.android.externalstorage.MountReceiver.onReceiv e(MountReceiver.java:30)

This reverts commit 98639167e2f6f6ddefc1358aff9f578ad87e5e17.