Apply suggestions from code review

Co-Authored-By: Povilas Versockas <p.versockas@gmail.com>

pkg/tracing/lightstep/lightstep.go

@@ -29,8 +29,7 @@ type Tracer struct {
 
 // Close synchronously flushes the Lightstep tracer, then terminates it.
 func (t *Tracer) Close() error {
-	lightstepTracer := t.Tracer
-	lightstepTracer.Close(t.ctx)
+	t.Tracer.Close(t.ctx)
 
 	return nil
 }