Remove errors.ConfdFatalError

This exception is caught, but never thrown. It became useless when we
moved confd from on/off to enabled/disabled, but always running on all
nodes. Removing its definition and the code catching it can do no harm.

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>