pack/debug: don't call the key server
pack/debug: don't call the key server

The debug packing was not supposed to call the key server for user
keys. The package comments implied that but weren't clear and this
CL clarifies them.

Any key will do; we use the user name as the key.

This package is intended to be simple and have no network dependencies,
so it can be used in tests with little infrastructure set up.

Restore that property.

Change-Id: Ib5e64c757a7f318115c20e888be8295b10cffe05
Reviewed-on: https://upspin-review.googlesource.com/2793
Reviewed-by: Eduardo Pinheiro <55040cbb39ba395339ae7940d8da6cd97797a4a8@google.com>

upspin/upspin,upspin/upspin