readme: remove outdated section about opentracing

README.md

@@ -55,20 +55,3 @@ func (r *helloWorldResolver) Hello(ctx context.Context) (string, error) {
 	return "Hello world!", nil
 }
 ```
-
-### OpenTracing
-
-OpenTracing spans are automatically created for each field of the GraphQL query. Fields are marked as trivial if they have no `context.Context` argument, no field arguments and no `error` result. You can use this to avoid unnecessary clutter in the trace:
-
-```go
-type trivialFieldsFilter struct {
-	rec basictracer.SpanRecorder
-}
-
-func (f *trivialFieldsFilter) RecordSpan(span basictracer.RawSpan) {
-	if b, ok := span.Tags[graphql.OpenTracingTagTrivial].(bool); ok && b {
-		return
-	}
-	f.rec.RecordSpan(span)
-}
-```