sim: update to new upspin interface definitions
sim: update to new upspin interface definitions

Many cleanups still to do, but this largely mechanical edit keeps
the tests passing while asserting the components satisfy the public
interfaces.

Change-Id: I3f7cc75e5170d59cf24c617b29b3a928ce56186d
Reviewed-on: https://upspin-review.git.corp.google.com/1050
Reviewed-by: David Presotto <516b9783fca517eecbd1d064da2d165310b19759@google.com>

upspin/upspin,upspin/upspin