chore(telemetry): code cleanup (#3897)

# What does this PR do?
Clean up telemetry code since the telemetry API has been remove.
- moved telemetry files out of providers to core
- removed from Api

## Test Plan

❯ OTEL_SERVICE_NAME=llama_stack
OTEL_EXPORTER_OTLP_ENDPOINT=http://localhost:4318 uv run llama stack run
starter
❯ curl http://localhost:8321/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-4o-mini",
    "messages": [
      {
        "role": "user",
        "content": "Hello!"
      }
    ]
  }'

-> verify traces in Grafana

CI

tests/integration/telemetry/conftest.py

@@ -23,7 +23,7 @@ from opentelemetry.sdk.trace import ReadableSpan, TracerProvider
 from opentelemetry.sdk.trace.export import SimpleSpanProcessor
 from opentelemetry.sdk.trace.export.in_memory_span_exporter import InMemorySpanExporter
 
-import llama_stack.providers.inline.telemetry.meta_reference.telemetry as telemetry_module
+import llama_stack.core.telemetry.telemetry as telemetry_module
 from llama_stack.testing.api_recorder import patch_httpx_for_test_id
 from tests.integration.fixtures.common import instantiate_llama_stack_client