veyron2/security: Get rid of FakePublicID and FakePrivateID.
veyron2/security: Get rid of FakePublicID and FakePrivateID.

Addresses one of the oldest TODOs in the codebase :)
In the process, also removes some types/libraries that will be rendered
useless once the switch to the new security model is complete anyway.

Change-Id: I5bfa5ef380832ce4b8c4370a83ea4f8a07507559

vanadium/go.v23,vanadium/go.v23,vanadium/go.v23