Throw when using deprecated file modes.

installd no longer grants o+x to private app data directories for
apps targeting N, so the long-deprecated MODE_WORLD_READABLE and
MODE_WORLD_WRITEABLE flags no longer have any effect, which may lead
to frustrating debugging sessions.

So to help clearly communicate that these flags no longer work, let's
throw when an app targeting N tries using them.

Bug: 26886867
Change-Id: I97dae6182fc3c55639ff37a39c4aae6dd0bed507