fix: remove stale .unwrap() in zipkin doc example

with_batch_exporter() returns Self now, not Result.

Assisted-by: Claude Sonnet 4.6

Author: lazureykis

opentelemetry-zipkin/src/lib.rs

@@ -179,7 +179,6 @@
 //!     Ok(trace::SdkTracerProvider::builder()
 //!         .with_sampler(Sampler::AlwaysOn)
 //!         .with_batch_exporter(exporter)
-//!         .unwrap()
 //!         .with_id_generator(RandomIdGenerator::default())
 //!         .with_max_events_per_span(64)
 //!         .with_max_attributes_per_span(16)