chore(telemetry): remove service_name entirely (#1755)

# What does this PR do?


## Test Plan

LLAMA_STACK_CONFIG=dev pytest -s -v
tests/integration/agents/test_agents.py::test_custom_tool
--safety-shield meta-llama/Llama-Guard-3-8B --text-model
accounts/fireworks/models/llama-v3p1-8b-instruct

and verify trace in jaeger UI
https://llama-stack.readthedocs.io/en/latest/building_applications/telemetry.html#

llama_stack/providers/inline/telemetry/meta_reference/telemetry.py

@@ -77,7 +77,8 @@ class TelemetryAdapter(TelemetryDatasetMixin, Telemetry):
 
         resource = Resource.create(
             {
-                ResourceAttributes.SERVICE_NAME: self.config.service_name,
+                # service name is always the same, use zero-width space to avoid clutter
+                ResourceAttributes.SERVICE_NAME: "​",
             }
         )