x/ref/services/mgmt/application: Remove impl directory.

Note that application/impl used to export ErrNotFound, which was
used by cmd/mgmt/device.  I've changed this to use the standard
verror.ErrNoExist error instead.  This will require us to update
the applicationd binary after submitting this CL.

Change-Id: Ibeeedd24d192d8f216e82ad7e08988bc987990bc
8 files changed