revert changes to the .env.example file

Author: Lingling Peng

.env.example

@@ -1,5 +1,6 @@
 ## Here are the environment variables you can set for the Synapse Python client to configure OpenTelemetry tracing and metrics:
 # You can copy this file to `.env` and fill in the values as needed.
+# OTEL_SERVICE_NAME=my-service-using-synapse-python-client
 # OTEL_EXPORTER_OTLP_ENDPOINT=http://fill-me-in
 # OTEL_SERVICE_INSTANCE_ID=local_development_testing
 # OTEL_EXPORTER_OTLP_HEADERS=# Authorization