Always use the local worker name in CreateWorkerSession when not doing ClusterSpec propagation.

Previously, the master would send a job name and task index in an
otherwise-empty ServerDef, and the worker would unquestioningly use
those to build its worker name. However, this would lead to errors if
the worker had a local name like "/job:worker/replica:1/task:0",
because the ServerDef doesn't support non-zero replica IDs, and so the
local worker would end up an inconsistent view of what its worker name
should be. In particular `WorkerSession::worker_name` would disagree
with the device names added during graph partitioning by the master,
which would lead to runtime failures ("InvalidArgumentError: Invalid
rendezvous key").

PiperOrigin-RevId: 193733855