interfaces: loosen a few max-size constraints which would limit us to a mere 1.09...

interfaces: loosen a few max-size constraints which would limit us to a mere 1.09 TB maximum file size

These constraints were originally intended to protect against attacks on the
storage server protocol layer which exhaust memory in the peer.  However,
defending against that sort of DoS is hard -- probably it isn't completely
achieved -- and it costs development time to think about it, and it sometimes
imposes limits on legitimate users which we don't necessarily want to impose.
So, for now we forget about limiting the amount of RAM that a foolscap peer can
cause you to start using.