Fix remove PendingTrace from span cleaner bug

dd-trace-ot/src/main/java/datadog/opentracing/PendingTrace.java

@@ -205,6 +205,7 @@ public class PendingTrace extends ConcurrentLinkedDeque<DDSpan> {
     while ((ref = referenceQueue.poll()) != null) {
       weakReferences.remove(ref);
       if (isWritten.compareAndSet(false, true)) {
+        SPAN_CLEANER.pendingTraces.remove(this);
         // preserve throughput count.
         // Don't report the trace because the data comes from buggy uses of the api and is suspect.
         tracer.incrementTraceCount();

dd-trace-ot/src/test/groovy/datadog/opentracing/PendingTraceTest.groovy

@@ -121,6 +121,7 @@ class PendingTraceTest extends Specification {
     trace.asList() == [rootSpan]
     writer == []
     traceCount.get() == 1
+    !PendingTrace.SPAN_CLEANER.pendingTraces.contains(trace)
   }
 
   def "add unfinished span to trace fails"() {